Coming from someone who doesn't like 25 man raids (I hated 40 with a passion), I am pretty excited to see that there's going to be less emphasis on which class you actually bring, and more on letting more classes be swappable, letting you bring your friends.
A buddy of mine (Cham, who played a mage) had a big problem with class stacking issues, and was always complaining about how useless he felt compared to my warlock. He had inferior damage, no summons or health stones, mana gems can't be passed out, and my lock had curse of shadows/elements. So what was he there for, then? Food? Heh. I couldn't help but agree with him, and it (among other things, like him watching me take on 3 people at once in a BG as SL/SL) eventually led him to getting burnt out on WoW via class envy. I can't really say I blame him, either. Playing a mage has never really tickled my fancy. I played a Wizard in EQ for far too long, and downtime is something that I absolutely loathe with a passion.
But getting back to the raiding issue: I also remember a lot of times we'd have to pass up someone who was more deserving of the raid slot that night (hunter), just so we could take a class that we really needed instead (shadow priest). Now, we won't have to make that choice. I like the fact that shadow priests no longer have the monopoly on raid mana regen.
I like where they are taking things, but again (and this is key), this is coming from someone who prefers 10 mans over 25 mans. And to be honest, I think that's where the eventual focus of raiding is inevitably going to fall when wow progresses past Wrath of the Lich King. I predict a big exodus of people from 25 man raids over to 10 mans, simply because it's simply a much bigger headache to lead and organize and satisfy 25 people than it is 10.
I really, honestly believe that 10 man raiding is going to completely overshadow 25 mans, as far as popularity goes. That's what's going to please most raiding customers, and I have a feeling that Blizzard is going to cater to them even more in the future after they see just how lopsided the preferrence really is.
So for me, I couldn't be happier. I can spend equal amounts of time doing PvP and PvE, without having to worry about running out of content after we finish 10 man Naxxramas, which will be our new entry-level Karazhan. No, I won't be able to pursue the uber 25 man trinkets to supplement my arena gear, nor will I be able to seek Frostmourne, as it will surely be a 25 man drop or quest line. However, I'll be able to comfortably enjoy both aspects of the game, without worrying about having to drop Player A, for a less deserving but ultimately more needed Player B.
I don't know about you guys, but I'm really excited for this expansion to hit. I have no doubt, from what I've seen this far, that Blizzard will nail it.