I posted this over on the EU forums as I was bored and a little fed up on my lunch break, I've added a few things to it based on things others have said and thought so enjoy the wall of text and stuff; just thought it might enjoy a slightly bigger audience here.
Right now, it feels like something has gone horribly wrong with the design of our class. There were issues - obvious ones - that I noted prior to Cataclysm's release, that simply haven't been registered, or have only just now been noted, and attempts made at fixing them put forward, which have in the process led to even more problems, which again, don't appear to have been noticed. I'm not about to quit the class over them as we're still playable, albeit frequently frustrating, and with a good number of out of place 'workarounds' in order to remain competative.
My first issue, is a pretty general one, and has annoyed the hell out of me since they were announced. It's our talent trees. We're completely talent starved, and at the same time bloated with mandatory DPS talents. If there were talents available for utility, we couldn't pick them up. The trees effectively allow for 6 builds, one each for PvP and PvE on each tree, with little or no wiggle room between the two. This is not the choice we were promised, and has made the cookie cutter specs of previous expansions more hard baked than before, not less so.
Furthermore, they are horrendously designed from a levelling perspective, with only Affliction actually offering anything as an insight to it's playstyle from the very first tier - Demonology is horrendous, with nothing but PvP and survivability talents in the first two tiers and a very minor buff to your pets' damage. Destruction is almost as bad with a second tier dedicated to high level spells and a buff to Searing Pain, which now we have Fel Flame is now almost a completely redundant spell in every aspect of the game.
My second gripe is our Demons. I love the notional idea of it not mattering which Demon we choose from a damage perspective, but instead choosing them based on utility. However, the implementation of the attempt is absolutely horrific. So bad, that the disparity between their outputs runs into the 1000s of DPS. The problem is the strange attempt to make Dark Arts optional, by making the Succubus viable via Glyphing. A nice idea in principal, but we don't actually have the spare, or optional talents to take as alternatives to make it a real choice. Dark Arts should be simply removed altogether, it is the worst kind of boring passive DPS increasing talent there is, as it doesn't do anything for your own numbers, and has no kind of interaction whatsoever. The fact that it's effect across demons is so wildly different just makes it harder to balance, and I see no reason why on Earth you'd even want to make a rod for your own back in that way; it's utterly nonsensicle.
Added onto this, we have the Mana Feed issue. Different pets will grant you differing benefits from this. Why? I don't get why the Succubus and Imp should be so much better for this talent, more than twice as good in fact, than the Felhunter and Felguard. It's a horrible implementation, and actually leads to the already wild differential between our pets' output making a bigger difference because having to use LT more because you're using FG or FH means you're spending less time using DPS spells. Why does it make a difference whether our pet is using a spell or melee swing to deal damage, and why does this matter with Hand of Gul'dan? It just feels like it's a part of an outdated design which probably made sense then, but the reasons for which have been long forgotten.
Related, is Demon Soul. Again, the different effects from different Demons is a nice idea, but it's adding yet another layer of complexity that doesn't need to be there. The different pets could offer different secondary stats (Haste, Crit, Mastery, and Spellpower), and they'd be different enough to be 'cool', but much more easily managable.
Third problem is our Masteries. Destruction is fine. Affliction is awkward, purely because of this idea of using Drain Life as a temporary filler during periods of high damage. Which again, is a nice idea - but it only applies to Affliction because it has the talents to make Drain Life a viable DPS spell in the first place. Destruction and Demonology aren't ever really going to benefit from that, so why make DL so powerful for Affliction that it's a viable DPS spell, and in the process cause obvious scaling issues with it's intended Shadow Bolt filler? Furthermore, it's actually leading Affliction to be arguably too good in certain encounters right now, as we move up tiers this will only get better and most likely lead to nerfing, as it's unlikely they'll change their encounter design philosophy just to accomodate one spec for being too potent.
Demonology's mastery is just bad. Against a backdrop of massive nerfs to Soul Fire and Decimation to redress the imbalance between the early stages of the fight and execute, it makes absolutely no sense at all to have Mastery bolster our cooldown so much. It'll cause a huge see-saw of damage between up time and down time at higher gear levels making comparisons to Wrath's Decimation seem tame. Furthermore, this will have a profound effect on PvP, where pressing that button would cause all kinds of problems with an incredible amount of burst damage.
Furthermore, such is Demonolgy's Mastery's implementation, that if you get a trinket proc during Meta, you receive no benefit, but if you wait and pop meta while the trinket is proced you'll get the benefit for the full duration. This is making a badly designed Mastery awkward to actually use, especially in working around a dynamic cooldown (which I love) which also can be a little awkward in certain encounters.
Our new spells too, Fel Flame and Dark Intent. Nice ideas, poorly thought out with no consideration for the consequences. Fel Flame has rendered Searing Pain and it's associated talent points almost entirely redundant, which they attempted to fix in a laughable and disasterous manner which in spite of so much discussion and simming totally took them by surprise when it went live. Dark Intent has added a needless throttle to our DPS output based on raid composition. I don't mind loosing some numbers because a raid buff is missing, and I don't mind a little added ramp up if it helps balance PvP, but I do mind loosing out because a couple of people didn't sign for the night's raid. It's a bizarre position, and I just don't get how it either slipped through or continues to persist.
All in all, these give an impression that the class is designed by a number of people who simply aren't communicating. A lot of very nice ideas, but badly implemented, ill thought out and frequently contradictory in terms of idea against overall design philosophy. Improved Soul Fire has been the central focus of that, and has actually caused these, and other issues to be glossed over and seemingly forgotten. It adds unnecessary awkwardness to the experience and puts people off not just the class, but the game as a whole and it's just not cool.
Anyway, that's the rant... discuss and stuff.
TL: DR This is not a discussion about DPS. Please don't go all "our DPS is fine therefore everything is fine there's more to the game than that.