I think first of all you need to look at what is meant by "exciting", if you mean huh this tree is pretty cool looking, or if it's like bam that's an exciting tree. I think the wording of this is pretty poor, realistically I think talent tree analysing falls into 2 categories: Core talents, and Utility talents.
Let's be frank with my feedback here, none of the talent trees are "exciting" in my book, since they are basically still the exact same way they were at 51 points, there are still going to be builds you can't have any choice over for pretty much every spec. The fact this question is being asked makes me think that a lot of the talent trees are finalised in terms of layout talents and such, and if this is the case then there was 0 point moving from a 51 point to a 31 point system, the same problems are still there with the talent trees.
Stuff like increased run speed is labored as a "utility" talent and is "optional" whereas as a hardcore raider I know that is anything but the case, run speed is a mandatory dps talent, like Metabolic boost is for zerglings in sc2, run speed=dps and is mandatory. Most of the talent trees at the moment are 31 points in your direct tree that you have absolutely 0 choice over, sometimes you are choosing between 2 different throughput talents and you can't have them all, this is wrong.
My "vision" for 31 point trees would be that you would have 25 points in your main tree that were mandatory for dps increase, this includes talents like run-speed aoe increases (because not every fight is patchwerk) and then you should be left with 5 points in your main tree you can spend on other utility things, such as Selfless healer in retribution or denounce in the holy tree, where there probably will be a "best" spec, but it would probably end up varying from fight to fight and beyond those 25 initial points might increase your dps by 1% at most, but more likely will give you utility to your group.
I think a prime example of the talent tree's failure is the talent impact, you called specifically for ideas on "utility" and I don't think it's too surprising people would give you ideas for dps increasing utility. At the moment impact is basically fire pestilence, obviously a bit rng but yeh, and that makes this talent mandatory, it is going to be a big dps increase on certain fights and does not in any way shape or form fall under the term utility in terms of raid utility.
Raid utility are stuff that don't directly increase your dps and are very situational, perhaps they help healers out with healing or are things that give you snare immunity or increase time on utility spells, stuff like incorperating the current glyph of evocation into a talent, thats purely utility. Many people would probably take it but only if the talent system fell under my criterion.
The idea here is so you end up needing to spend about 4 points on average per tier and then have 1 extra point per tier (maybe 2 or none per tier but on average 1) where you can put into any talent you have access to and it be "ok".
My main problem with talent trees are there are going to still be plenty of talents that never see the light of day outside of say levelling, denounce is one of these in Holy's current status, you just don't have any room to take this interesting utility talent, it obviously doesn't affect healing throughput it's just utility but I can't take it because I don't have enough points.
My biggest qualm with talent trees right now are the subspecs. I realise Blizzard wants to encourage subspeccing but ideally I feel people should have loads of choices with their subspec options, if something that is "mandatory" for dps is in the second tier I have to devote 8 points to that tree, you may argue that you can choose between talents in the first tier (often this isn't the case and people need "motivation" to spend talents in the first tier to get to the second tier) but well surely it's better if there are around 5 mandatory points in subspecs, that were all in the first tier. Lets say for shadow we had evangelism and Archangel in the first tier and then twin disciplines a 2 point talent in holy and then some talents in shadow main tree clipped, ideally you would end up with a cookie cutter spec which is like
3+x/2+(5-x)/25+6 where you get to choose the plus talents completely freely, right now in pretty much every tree the talent tree cookie cutters are like 31/8+x/(2-x) where you basically have a maximum of 2-3 points you can choose from, and even then thats being generous. I'll try and list the "best" trees that fall under this criterion.
1) Shadow Main tree
I've already commented on how this tree doesn't really work for levelling because of mana issues, but if we ignore this we get a pretty good tree, you end up with 4 points to choose between utility talents, you could grab silence and psychic horror or you could grab the free pvp trinket or a stun or whatever, you have a lot of choice in the shadow main tree. This is exactly how I would hope to choose my max level spec (obviously whilst levelling this needs tweaks but thats more rearranging talents that are mandatory and the same cost rather than anything major).
However if we look at the subspec options we just don't have any, all 10 points have to into discipline, 8 points are already mandatory in discipline, and 2 points extra in the second tier all have dps consequences so really you only have 2 points to choose between mental agility and improved power word: shield, which isn't enough.
2) Fire Sub-spec
I want to make it clear that this is about Sub-speccing options, the actual fire tree is poor because you don't get any choices for utility (unless you consider impact utility) and you have to actually spend 32 points in the tree to get all the dps talents you want.
However, looking at the subspec options of the tree they are probably one of the most ideal, you have 3 points you *need* to spend in arcane/frost (that is netherwind presence/Piercing Ice) then you have 4 free points you can spend in either tree or back into the fire tree on pure utility and not on dps increasing talents. Obviously I feel like netherwind presence and Piercing Ice should be 2 point talents, (or even removed since these are talents which are supposedly boring). This assessment also presumes that arcane concentration is in no way mandatory for fire mana conservation. If it is then this sub-spec is again worthless.
I want to note these are all from a pve stand-point, in my opinion pvp is useless and shouldn't influence choice on talent trees, obviously utility talents have far more use in pvp than in pve. I also want to note that I do not consider purely threat talents in a tree utility unless they are an increase to aoe threat, numbers are not finalised so I cannot tell how mandatory those talents would turn out being.
Other trees which are pretty good:
Beast Master Hunter Main-tree
Arcane Mage Main-tree
Fire Mage Subspec-tree
Frost Mage tree (some talents need work but overall the feel is good, subspec is pretty good aswell presuming frost doesn't need master of the elements and arcane concentration)
Retribution Paladin Main-tree
Holy Priest Main-tree (If Test of Faith is changed to 2 points)
Shadow Priest Main-Tree
Combat Rogue Main-tree
Subtelty Rogue Main-tree (Presuming that Energetic Recovery is not Mandatory, Cheat Death is Reduced to 2 points)
Elemental Shaman Sub-spec Tree (I'm torn on this, 7 mandatory points is too much but you have good choices with the 3 remaining points, it remains here but it's borderline)
Affliction Warlock Main-Tree (If everlasting affliction is a 2 point talent)
Demonology Warlock Main-Tree
Destruction Warlock Tree (Very good tree (from my limited understanding of Destruction Warlocks)
Destruction Warlock Tree (Very good tree (from my limited understanding of Destruction Warlocks)
Arms Warrior Main-Tree (Improved Hamstring needs to be 1 point or a talent below it only 1 point otherwise this can't be taken)
Fury Warrior Main-Tree
Protection Warrior Main-Tree (Borderline.. I say this is ok presuming aoe threat isn't mandatory but you can't get all of the aoe-threat talents as utility so it needs some tweaking but is "ok")
Trees which need to be changed:
Blood Deathknight tree (Choosing between throughput talents in main and subspec)
Frost Deathknight tree (Only 1 choice at tier 2, rest is mandatory)
Unholy Deathknight tree (Choosing between throughput talents)
Balance Druid tree (IF Owlkin Frenzy procs on all attacks, this tree needs work... if not then it is ok IF Moonglow is not required for boomkin mana regen, subspec is all mandatory)
Feral Dps Druid Tree (All mandatory, no subspec balance options & mandatory 8 points in Resto)
Feral Tanking Druid Tree (All mandatory, arguable that kotj is utility but that's the only thing you can spend points on, subspec options all in resto but amount of choice is good)
Restoration Druid Tree (Far far too many mandatory talents in resto, I had to spend 5 extra points to get everything, subspec options offer no choice)
Beast Master Hunter Sub-spec Tree (no choices at all)
Marksman Hunter Tree (All Mandatory and too many talents, no choice in subspec options)
Survival Hunter Tree (All Mandatory and too many talents, no choice in subspec (presumably I don't have enough knowledge of survival hunters to know for sure))
Arcane Mage Sub-spec Tree (8 mandatory points, little choice beyond that)
Fire Mage Main-Tree (Way too many mandatory points, probably want to spend 35 points in the tree)
Holy Paladin tree (All Mandatory talents in both main and sub-spec trees)
Holy Paladin tree (All Mandatory talents in both main and sub-spec trees)
Protection Paladin tree (Way too many choices of Mandatory Talents in both main and sub-spec trees)
Retribution Sub-spec tree. (8 Mandatory talents with little choice available for the remaining 2)
Discipline Priest Tree (Absolutely no choice, all talents are mandatory in both main and sub-specs)
Holy Priest Sub-spec Tree (This is here because there are 8 Mandatory talents, the choice between the final 2 is pretty good though)
Shadow Priest Sub-spec Tree (All talents in sub-spec are mandatory, you even choose between 2 throughput talents, nothing in holy is worthy of sub-speccing)
Assasination Rogue Tree (Presuming Back-stab is an execute ability all talents are mandatory (Movement speed is not utility), choosing between dps increasing talents in sub-spec)
Combat Rogue Sub-spec Tree (Considering run-speed is mandatory and that eviscerate is used in combat rotation 0 choice in sub-spec)
Subtelty Rogue Sub-spec Tree (Considering Run-speed is Mandatory, no choice in sub-spec)
Elemental Shaman Main Tree (Way too many Mandatory Talents)
Enhancement Shaman Tree (No choice in Main-spec or sub-spec, (regardless of if primal wisdom is or isn't mandatory)
Restoration Shaman Tree (No choice in Main-spec or sub-spec, (Elemental Precision needs to be available and not mutually exclusive with Movement speed))
Affliction Warlock Sub-spec Tree (No choice at all)
Affliction Warlock Sub-spec Tree (No choice at all)
Demonology Warlock Sub-spec Tree (All Mandatory points, choosing between way too many dps increasing talents)
Arms Warrior Sub-spec Tree (This is dependent on Enrage stacking with wrecking crew, if it does it's bad, if not then the sub-spec tree is "ok, but could use some tweaks")
Fury Warrior Sub-spec Tree (Deep Wounds is far too mandatory to be 2nd tier and 3 points, should be baseline and removed, then sub-spec is perfect)
Protection Warrior Sub-spec Tree (Too many Mandatory Talents to choose between)
Hopefully this comprehensive list of opinions tells you what you want to know, the best tree at the moment is the Destruction Warlock Tree in my eyes, whether you call it "exciting" is very different because I don't think "exciting" quite cuts it, all the trees are pretty exciting but this tree is the most well made and allows for the best freedom of choice whilst remaining as exciting as some of the more bloated trees.