As I listed in this post:
With the expansion just under a couple of months away, I wanted go ahead and put together a list of concerns that I, and others, have with this class at this point in time:
1) Runeforging. We already have a blue thread on this, but hopefully this perk to the class will end up being more fun and exciting than just another set of enchants. This particular mechanic had so much potential, but this is the one area that I firmly believe didn't receive enough planning from the get-go. I really liked Hadassa's post about runeforging (found here:http://forums.worldofwarcraft.com/thread.html?topicId=8202576984&postId=82017104353&sid=2000#0). I really wish Blizzard would be able to find the way to implement something like this in the future, if right now it's simply not possible.
2) The Ongoing debate between 2H vs DW. Personal bias aside, it would be wonderful if these two could coexist peacefully and always be equally viable at every step of gear generation. Unfortunately, given the history of gear progression with classes that have the option to dual wield, I see this being a very difficult thing to balance with regards to making both equally viable at all times. While it's normal for some specs' relative power to fluxuate as gear and encounters progress and change, usually one spec or playstyle ultimately wins out in the end. That, I believe, is the main concern on everyone's mind: In the end, which style is going to produce the higher DPS? Few are really concerned with how things are performing right now, but more concerned with how things will be performing in the future when the class's mechanics are in a much more fixed state, in relation to class balance in all aspects of PvE and PvP (where it's much more difficult to change class fundamentals if things don't work out to be balanced for 2h vs dw in the end).
3) Tanking viability. This one is pretty huge, and probably will get overall more visibility than any other issue (and rightfully so). There is a fairly large concern that I see popping up over this forum, as well as others that I follow, that DK tanks are not quite up to par with the others as of yet. As of right now, the threat seems fairly low, which essentially has everything to do with our DPS reductions, as we rely on far fewer innate bonus threat modifying abilities to generate and hold agro (with the exception of D&D). But I have to ask: As far as D&D is concerned, should it really be that way? Are imaginary inflated numbers more fun to use than actually doing more damage? Of course not. Ideally, all tanks would be more fun to play if they did generated more threat via doing more damage, rather than spamming buttons that apply debuffs that generate invisible +threat numbers to build hate that you can only see via 3rd party addons (Example: Sunder Armor vs Devastate). Doing damage is always more fun. That seems to be one of the main philosophy shifts that this expansion brings to tanking, and one that I welcome with open arms.
However, getting back to the main point, DKs seem to have lower armor than most other tanks, as well as a smaller health pool, in addition to relying heavily on avoidance without having fall-back talents such as ones that grant crit immunity early on (such as the talents druids can spec into, for example). This means that the damage we take between cooldowns and avoidance RNG procs is actually pretty high, and hurts undergeared DKs more than any of the other tanks. However, while think DKs might have some issues of tanking viability early on, I think that they might actually end up scaling with gear well enough in the later stages of content to at least be equal with the other tanks. This is mostly in part to things such as ridiculous amounts of STR on tanking gear now (thank you!), coupled with core abilities such as forceful deflection (another suggestion implemented via feedback here). Also, when our damage is balanced (raised a bit in relation to others right now, or have everyone else's lowered), our threat will be too. I'm not too concerned with threat right now, as our threat ties directly into the damage we do.
4) PvE DPS viability. I won't say a lot on this topic, as the numbers (and to a lesser degree, the talents) are still in a state of flux right now. I'm not sure where the final numbers will land, along with our place on the DPS meters, but hopefully they won't be too much lower than the pure DPS classes. Do I expect to do as much or more DPS than a destro warlock, hunter, or rogue on single fights? Or as much damage as a mage on AOE fights? Of course not. Right now I'm hoping that I can pick the playstyle of DK that I like and be at least as competitive as a DPS warrior or enhancement shaman, however. Blood DK's seem to have excellent single target DPS potential, while Unholy DKs seem to bring a lot of AOE potential. In fact, Unholy DKs seem to be the premier support class for helping your magic-users AOE down trash that much faster due to ebon plague + unholy blight. However, I'm wondering then how useful those unholy (or frost, for that matter) DKs will be on single target (i.e. boss) encounters will be. Frost, on the other hand, is just doing too little damage right now. Both Howling blast and Frost Strike are doing roughly 33% of the damage they did a couple patches ago.
5) PvP viability. I already wrote up a pretty lengthy post about this here: http://forums.worldofwarcraft.com/thread.html?topicId=9336502308&sid=2000, and my position hasn't really changed much on this issue at all. While the damage/dps numbers have changed since then, the actually mechanics really have not. Thus, my opinion still holds.
Edit: Blue response.