I guess what I want is some variety in 5-mans, beyond straight paths with trash between bosses. I know BRD gets a lot of shit, but there were so many ways through it you kind of picked your own adventure. For example, there are rooms I was in on my last BRD run that I'd never even seen before.
I'd like to see "Adventure" Dungeons that are more non-linear, take more time, and have ramped up difficulty. The rewards could just be more badges, but because of the layout, they're not easily farmed. One really great part would be having each dungeon built similar to Phantasy Star Online's dungeons; some doors are sealed off, some ways are closed, and it more or less randomly picks a new layout (from half a dozen or so).
I guess I want to feel like dungeons matter again instead of just being scripted dance routines people rush through. In Vanilla we did BRD (and UBRS when it switched over from a raid) all the time, just because there was so much loot down in those places and you didn't have badge gear to automatically get you maxed out eventually. In Vanilla, 5-mans were pretty much as far as most people I played with were happy to go, because they were still challenging but you didn't need to organize people.
I'm not one of those "OMG, Vanilla wuz bettur, classik survurz plz" people, but some aspects of the game were better, at least in my opinion, back in those days. Maybe not for everyone, but I was always content with 5-mans. After doing ZG before TBC launched, going as far as Kara and Grull after, I kind of lost interest in raiding. It was only because of the guild I was in that I bothered with raiding in WotLK... I've done Naxx, I've done Ulduar, and I tried ToC (burned out about that point). Raiding just doesn't interest me, and if it did I'm past being burned out on that kind of scheduling anyways.
That's not to say that Raiding needs to go away, I just wish there were alternatives. Sadly, Heroics and 5-mans are basically just loot farms to direct you towards raiding, so they're not built to be as interesting as they once were. I guess I just want that kind of experience back, though I know there's no way it's going to happen.
Luckily, I've found that I'm quite happy with just rolling alts and Cataclysm will deliver at least two new experiences on that front (both Alliance and Horde leveling experience). I also like lower tier PVP now that twinks have been isolated and contained, and anyone who does twink quickly moves out of their bracket (or at least, I will). So, there's always that.
I've always loved the dungeons in the game, though, and I guess I just miss that being an acceptable goal. By that, I mean the way that Blizzard approaches their design. They've nerfed a lot of old bosses that really didn't need it just to speed things up, and the dungeons were already really straightforward as it was. Their attitude now seems to be "Get to 80 so you can run 5-mans so you can run heroics so you can raid now now now." I can't be the only one feeling it.
If they could implement PSO's Challenge mode somehow, I'd be happy as a pig in shit.... :lol Good luck of that ever happening ("OMG, why am I level 1! Where are all my epics! You mean we have to work together?!").