Just thought I'd chime in here. Been playing a whole bunch of AoC since the Early Access started on Saturday and have had a blast with it. For reference, I've played EQ, AO, DAoC, EQ2, WoW, Guild Wars, and a few others extensively. AoC really does beat the crap out of them, so far at least. I'll just do a quick bullets on my experience so far.
Tortage/Instancing: First, I'm just going to say it: you don't have to kill a single freaking rat, snake, piglet, wolf, or tiger. I love Funcom for this alone. Tortage is the starting city, where you do the first twenty levels. When people complain about the game feeling like a single-player, it's because a lot of the quest content at the noob levels is instanced. The basic way it works is that there are two types of quests: your normal MMO quest that take place during the day and the Destiny quests that take place at night. Daytime content is semi-instanced much like cities in Guild Wars, where each zone has a certain number of people it can contain, then it spawns another instance. There's a button on the mini-map that lets you select which instance you want to go to so you can join friends or leave an instance that's too crowded for your tastes.
Anyway, the Destiny quests are actually a lot of fun. They do feel like a single-player game, but they're heavily story-driven and because all of the content for them is instanced, the quests will always run smoothly and you won't have to wait around for a spawn. You can easily switch back to daytime if you want to just run some random quests or run around and grind with friends.
World: The world is huge. Really. The zones themselves are quite big so once you leave Tortage, so you won't find yourself zoning very often. Load times between zones are roughly the same amount of time it takes you to run through transition areas in WoW, usually 2-5 seconds or so. In terms of design, it's very different than most of the games that are out now. The scenery is pretty lush, and I'd call the overall style sort of a gritty realism. The jungles and forests are pretty, and the battle grounds look like real battlegrounds with dismembered bodies and puddles of blood laying around. You'll also find bodies and heads impaled on spikes, and if you go to the northern part of Conall's, you'll even get to find the hanging tree, with probably 10 or 12 bodies being hanged, a bunch of crows flying overhead, and another pile of corpses on the ground with flies buzzing around. Very much not WoW-cartoony. That said, some of the pathing is a little annoying every once in a while, and one of the resource-gathering zones (Lacheish Plains) seems to be very bugged and will make you crash repeatedly until you leave the zone if you spend any time in it.
Combat and healing: Really fun. Actually feels a lot of like old-school Streetfighter or Mortal Kombat sometimes when you're using your combos and switching them up to get around the other guy's shields. As a former WoW raider, I can probably best sum up combat and healing like this: it's impossible to watch TV and play AoC at the same time, i.e. if you're healing, you can't watch health bars out of the corner of your eye while you watch. Both combat and healing are too active and require a great deal of micromanagement. Healing, you need to keep your two HoTs up at pretty much all times, then help mitigate damage through your own DPS, stuns, knockbacks, and CC while saving your burst heal (30 second cooldown) for real emergencies.
Combat, you need to watch your enemy's shields (NPCs only, really. Too much micromanagement for players to worry about them now, while we're all still learning the game). The shields mitigate a ton of damage, and popping your biggest combo on a side that has all three shields will get you about a third of the damage you'd normally do. Crits happen, but the game doesn't seem to be very crit-dependent, which is nice as it reduces the luck component. No idea if this changes at higher levels, though.
PvP: Still too early to tell, honestly. All classes and specs seem viable for PvP so far, and pure PvE specs like healing and tanking in WoW are flat-out impossible. Everyone can do DPS and everyone is expected to. The fights I've been in (level 33 now) have been a lot of fun, and skill in choosing your combos and supporting each other correctly makes a huge difference. Again, though, no one's 80 yet (well, not without exploiting) and there aren't enough people high enough to get a real sense of the classes yet. Based on experience so far, I'd say I'm cautiously optimistic.
Anyway, need to wrap this up, but overall I'd definitely say the game had a great launch with a few hiccups. It's been nice and stable all the time, with the only crashes I've had in the bugged zone. The game seems to almost always crash shutting down, though. Annoying, and something they'll hopefully fix soon.