I've come to think of some little things that would make me enjoy the game even more. It's not about spells or class balance but instead of the social aspect and of tracking completion or achievements in the game.
Starting with the social idea, I think it would be very nice if I could see how my friends look and what gear they are wearing just by clicking them in my friends list. I mean exactly as it looks when using the wardrobe to preview gear. A players appearance is based on a few choices at character creation and the gear is just a couple of items with an id. It shouldn't be that hard to fetch and preview, it doesn't really have to be in real time, it could be based on the last armory scan.
I came to think of this because at least in a 25 man raid it's easy to be zoomed out most of the time for practical reasons. I like to zoom in on players while waiting to start to see how they really look. A function like this would make it even easier to recognize and learn your friends appearance and I think that in role playing games, looks are a very big thing. It did sound silly when Blizzard introduced 'Changeable hairstyles' with the same dignity as 'New continent: Northrend' and 'Death knight' but I think it's a big deal to add more personality and choices to the characters. I think looks matters in-game and I'd like be able to look more at my friends without having to be near them for practical reasons.
Shouldn't there be more to a player than what meets the eye? So far the game is only tracking what you've accomplished by showing what you are currently wearing. I'd like the game to track completion when it comes to dungeon- and raid sets worn and bosses killed. Imagine a new tab when inspecting a player called Completion or Achievements or something. You would for example be able to see that this rogue had 8/8 of the Bloodfang armor or that paladin had the full Judgement set at one time. Let each gear piece and boss kill amount to a certain score and it would be an excellent way of measuring individual PvE progress because PvE is a very core part of the game isn't it?
The last part of tracking progress would be to see what bosses a player has killed. Self-explanatory really but if you've cleared Blackwing lair, wouldn't it be nice to show that in another way than wearing an obsolete drop from Nefarian which also takes up inventory space? Gear is mostly about stats but it's also a marker for what you've achieved. When expansions arrive the achievements are sort of deleted as it is implemented now. I think much frustration from end-game raiders when it comes to new quest greens replacing epics comes from no longer being able to show the results of their efforts.
It's natural for an expansion to replace the old content and for the players to move on but I think it's a bit cruel towards the players to not track the efforts. Maybe not everyone thinks of it in this way but at least I do. I really enjoy the encounters and I get satisfaction from completing difficult encounters and by playing together with friends. It's only a game but for what it's worth I'd like the actions in it to be a bit more persistent.