Legion is a great expansion. In fact, as I've been saying for a while, if they keep things up, we might finally see Wrath of the Lich King dethroned as it were (I know that "best" is a very subjective term, but personally I think the amount of content, accessibility, new gameplay and story were all precedent-setting in Wrath.)
Obviously one of, if not the biggest feature in Legion, and the one that is likely to have the biggest longterm effects (PvPers might cite the new Honor system instead) is the new class, the Demon Hunter.
Having now gotten to a point where players might actually have well-geared Demon Hunter mains, or at least high-priority alts (mine has more or less become a solid number 3 behind my Main Paladin and Chief Alt/Vice Main Death Knight) I think we can talk a bit about how well they're working out.
Story, Flavor, and Lore:
Obviously as a Hero Class, Demon Hunters have a lot going for them. While Death Knights had a very big presence in Wrath (though they shared center stage with Paladins and arguably Mages,) the Illidari are a big presence, but not a ubiquitous one. They've managed to feel important without really hogging the spotlight, but I think that's more about the wonderful focus on class content: in effect, every class feels important in Legion. Demon Hunters just get a few areas to help establish important Demon Hunter characters.
So, speaking of characters: There are a lot of DH characters who pop up as recurring names and faces. Demon Hunters of course have these as class champions. That being said, I don't know if they've done a great job of really introducing them.
Death Knights basically had three NPCs that everyone knew and interacted with. Darion Mograine was the Death Knight counterpart to Tirion Fordring and was the public face of the Ebon Blade as a force for good in the world. Then you had Thassarian - a man of honor with a family to protect and loyalty to his friends who was somehow kind of a good guy even when he was part of the Scourge (he saw undeath as an escape from racism and prejudice, sending you to rescue Koltira.) And of course you then have Koltira, who represented a somewhat colder and callous attitude, but backed it up with great competence and knowledge.
I can't really say that any of the Demon Hunter NPCs have made such an impression. We have yet to find out what the consequence of choosing Kayn or Altruis at the end of the starting experience will mean, and most of the characters are kind of generically broody. I'd like to see more of Korvas, the woman whom you fight alongside on Faronaar and who is the subject of the Illidan Harbinger video.
Really, I think this is one of those situations where they had to create a number of characters to give you enough champions, but a lot of them aren't terribly fleshed out.
There's also a big question, which is what will happen if and when Illidan makes his return. Demon Hunters are part of the Illidari, and so one imagines they'll be working closely with him if he returns to the world of the living. But I also wonder if that will then make the Illidari story really just the Illidan (and some friends) story.
Havoc feels very different from any melee spec that has existed before, largely due to the power of Fel Rush. An ability that you'd expect to be a kind of utility spell, this instead is a serious part of your DPS - though I don't know if that's true for all talent builds.
See, the thing about Havoc is that the talents you choose make such a big difference that I don't know whether there's a lot of flexibility. For example, while I've gotten used to it now, I wasn't really crazy about Bloodlet - a talent that makes your Throw Glaive ability apply a very strong bleed. But combining Bloodlet and Momentum (which gives you a damage boost for a couple seconds after Fel Rush or Vengeful Retreat) has such incredible synergy (Bloodlet's damage is based on that of Throw Glaive, so the short-duration Momentum damage boost gets effectively extended over the course of the whole bleed) that I don't know that you can choose any other talents in either row. Then you get Fel Mastery and Prepared to further boost the use of these Momentum-activating abilities, and it starts to feel cookie-cutter.
Synergy is pretty cool with talents, but when it's too strong, or there isn't a competing synergy, you might wind up stuck with one "right" way to play the spec.
Now, I haven't done a bunch of theorycrafting research recently, so maybe there are other options out there, but for now, it seems as if there is one good way to spec Havoc.
Of course, thankfully, it's a lot of fun.
I guess the only other problem is on-demand AoE. You can have nearly unlimited cleave thanks to Bloodlet, but for true AoE, basically everything is a cooldown - Fel Rush, Blade Dance, Eye Beam, Fury of the Illidari - all of these are tied to cooldowns.
Still, they're so powerful that it's not really that much of a problem.
Overall, Havoc is tons of fun, and these are only nitpicks.
I remember people worrying that Vengeance wasn't tough enough, but I'm not finding that to be much of an issue. Being used to playing my Paladin and Death Knight, I do notice the lack of a stun, but it's not that much of a problem.
Vengeance does a lot more self-healing that I figured the DH tanking spec would. It's probably not quite up at the level of Blood Death Knights (where self-healing is basically their primary tanking strategy,) but it's very high.
One thing that can sometimes be frustrating is that the amount of self-healing varies significantly. You're really at the mercy of Soul Fragments - getting a couple of those elevates a Soul Cleave from a significant, but really just moderate heal into something almost like a rotational Lay on Hands.
Sigils are cool, but honestly, the one that I'm least happy about is Sigil of Flame. It's not quite like Death and Decay, which creates this nice persistent AoE that is great at catching streaming adds (though nothing beats Consecration for that!) and one could make a pretty solid argument that between Infernal Strike and Immolation Aura (and Throw Glaive for cleave situations,) Vengeance doesn't really need Sigil of Flame. I have the talent that causes Infernal Strike to create Sigils of Flame, meaning that a lot of the time I don't have to manually cast it.
I suppose the one other issue is that sometimes, the rotation kind of falls into a section of "spam Shear." Both DH specs are GCD-locked, with a no-cooldown generator ability. But Havoc can really break up its Demon Bite spams with things like Fel Rush - in fact, I sometimes forget to use Demon Bite given how much Fury I can generate with Fel Rush and Prepared-talented Vengeful Retreat.
Still, while there are other sources of Pain, sometimes you want to spam Shear anyway to get some Soul Fragments.
Still, in terms of tanking capabilities, I'm pretty happy with Vengeance. You have a very reliable (long duration, relatively short recharge and low cost) active mitigation ability. There's plenty of threat coming from your Immolation Aura and Soul Cleave is not bad for snap-threat. Throw Glaive is practically always available to get distant adds, as is Infernal Strike.
There aren't a ton of big damage-reduction cooldowns, though I honestly don't find myself hitting Metamorphosis that often (I do have a talent that sets it off automatically if I'd otherwise die, and of course there's an artifact trait that gives it to you for short durations periodically in combat.)
As someone who plays a Paladin and a Death Knight tank, Vengeance's mobility is really exciting, though I wonder if people who play more with the other tanks feel that as much. Vengeance doesn't zip around the battlefield as much as Havoc, but that's probably for the best, as melee DPS would hate you.
Demon Hunters make my Death Knight jealous. DKs, mind you, were unprecedented in having things that distinguished it from other members of that same race. You got glowing blue eyes (less impressive on my Draenei,) your voice got pitched down (making the clattering sound effects in that one male Draenei joke sound super weird) and you got some special rotten-looking skin and face options (unless your race is Undead, who, well, already look like that.)
Demon Hunters are practically a different race (well, two.) Not only to you get horns, a blindfold, glowing green eyes (if you don't go with a blindfold - but this glow goes way beyond the standard Blood Elf glow) as well as scaly or fel-lesion-pocked skin, but you also get a somewhat different face (Night Elf males all get a kind of sneer) and even a bonus hair color (I don't think other Night Elves can get totally black hair.)
But the biggest thing is the voice acting. Demon Hunters have totally different voice acting, along with their own jokes and flirts
We have yet to really see a ton of Demon Hunter armor. So far, we've got basically two questing sets from the starting experience, then the class hall set and the first tier set.
But then we also have a totally new weapon type. This is something I really wonder about going forward. With artifact weapons, it's no problem at all to give DHs Warglaives without worrying about if other classes should get to use them. But in the next expansion, are Demon Hunters going to be forced to use simple swords and axes? Warglaives are a huge part of the aesthetic, but when weapons aren't designed specifically for the class, will Demon Hunters who want to use their glaives be forced to transmog to the few models introduced in Legion?
Into the Future:
I'd really have liked to see more races made available as Demon Hunters. The question is whether that can really ever happen. Basically, unless Naga, Broken, or Shivarra (somehow) get added as a playable race, there's no one else who would appropriately be at the Black Temple to start the Demon Hunter experience at the appropriate time.
I doubt we're going to see a third spec added to the class. In fact, I even suspect that future classes will probably have just one spec per group role (I also highly doubt we'll see any new pure DPS classes.) While I think a ranged dps spec for Demon Hunters could have worked (and would have been the first ranged spec added since vanilla) I think having just the two has actually worked out just fine for the class.
Most classes have undergone huge changes over the years, and so I certainly won't count Demon Hunters out on that count. But for now, things seem to be going well.