I played the WoW open beta for ten days and I'm impressed enough that I have the Collector's Edition pre-ordered and paid for. It's incrementally better than all the other MMO's I have played. There are few revolutionary ideas, this is still an MMO, you still battle critters to gain experience to learn skills to use when battling bigger critters. The most important difference between this and EQ, DAoC, FFXI, and others is the "Blizzard" name stamped on the front, and the Blizzard design philosophy that permeates every element of the game.
In one word, that philosophy is "Polish".
I've played a lot of MMOs at release and none of them looked half as complete as this game. DAoC had tiny realms with few quests. EQ had broken quests and game mechanics (and an inflationary economy borrowed from Germany circa 1928). Anarchy Online was a slideshow and literally unplayable for the first month or so. WoW, in contrast, is playable, full-featured, teaming with life (and undeath) and provides even the lowest level characters with fun things to do. Most MMOs NEVER reach this stage of development, and the few that do take a year or more of patches past release to accomplish it.
If you have played other massively multiplayer games the experience of WoW is revelatory- time and time again you stumble across some feature or gameplay element that's been improved from other games, and the Blizzard solution is so simple and obvious that you wonder "Why the hell didn't anyone think of this before?" Take the crafting system- EVERYthing you make can be sold, to the vendors, for a profit (assuming you gather your own materials). Not one or two things at a given skill level, EVERYthing. You never fail when crafting- you can either make the item, or you can't. Oh, and if you want to craft 10 elixirs of minor health, you just enter in '10' in a little box and click create and your character will keep crafting until he makes ten- no more dragging items into a crafting dialog box one at a time and clicking 'Create' for each damn item. This transforms crafting from a damnable chore (DAoC) or a great way to throw away money (EQ) into a really fun experience. I must have spent half my time in the game working on crafting skills.
The past two weeks saw the release of Halo 2 (which I've defeated), Half-Life 2 (which I've played a few hours in), Metroid Prime 2 (I've just started this), and MGS3 (haven't grabbed it yet). All that, along with time on Halo 2 Live, building my new computer, and going to work everyday... well, I didn't have much time to spare for WoW. Still, in the short time I had (and spending 50% of my time on crafting and goofing off) I was able to achieve level 13. Gaining experience is pretty easy.
First, your character is a lot stronger than characters in other games, relative to the critters you fight. In WoW my character can fight two creatures my same level and win with little trouble. I can fight three and win if I pull out all the tricks, or I can take on a creature two or three levels higher than me (and worth a lot of XP) and expect to win. It's great not to feel like a wimp all the time. Second, every class can solo through the game. If you don't like to party, or if your usual crew isn't playing at the moment, no sweat- you don't need 'em. Third, the downtime is virtually non-existent. My Rogue could get down to 30% health in a battle and in the time it takes to find the next target- ten seconds or so- I'm back up to full health. That's running around, not sitting on my ass staring at the scenery. Now, to be honest, most classes have a LITTLE more downtime than that, but not much, and there are many ways to speed up the health-and-mana recovery process. All this means you're much more willing to take risks and try new things... as long as you're smart and not fighting things more than three levels above you it's possible to fight/flee your way out of a jamb.
What if you do get splattered? Hell, WoW even makes death a fun experience. Cemetaries are scattered across the world, and when you die you re-appear as a ghost in the nearest. Now you have several options. In the cemetary (visible only to the recently departed) is a creature called a Spirit Healer, and she can resurrect you immediately... but you suffer a temporary stat loss, and your equipment become damaged a bit. If you don't like that noise, you can run back to your corpse as a ghost... and this is the great part. The Dead world looks like 'Wraith-World' from Lord of the Rings... everything's black and white, there's an unnatural wind (cool effect, looks like a giant maelstrom in the sky trying to suck everything up into it). As a ghost, no one alive (almost) can see you, and you can't see anyone alive- only other ghosts, and corpses. You see no enemies. You can run on water. It's a blast just looking at the wraith-world, almost worth dying just to experience it. Once you get back to your corpse, you hit "Resurrect" and all goes back to normal... you lose some "durability" on your items, and the time it took to run back to your corpse, and that's it. No XP loss (or debt, or whatever). At high levels death is expensive- you have to pay to repair your uber-items- but at low levels it's nothing.
Let's talk about graphics. WoW follows the Blizzard philosophy that skill and artistry is more important than technical prowess. The game is easy on system requirements (only requires a P3 800 and a 16MB video card, or so they claim). While there are a couple of high-end options you can turn on if you have a recent video card, the game runs beautifully on mid-range and even some low-range systems. As with all MMOs the most important requirement is RAM- make sure you're packing 512MB to run the game smoothly, and if you have 1GB it'll handle even the busiest zones without significant framerate issues.
Despite the less-than-cutting-edge graphics engine the game looks jaw-dropping beautiful. The character models are full of personality- cute and spritely if you're a gnome, mysterious and sensual if you're a night elf, disgusting and creepy if you're one of the undead. ALL the creatures in the game are equally well designed- from squirrels to ogres to mechanical exploding sheep (yep, they're here!) They look great and they move convincingly. Even better than the creature models is the world itself- it's gorgeous and stuffed with personality. Entering Ironforge for the first time was just joyful- it's brimming with life and creativity. The effect is not photo-realism, but rather a kind of story-book whimsy. Running side-by-side, EQ2 will look more impressive at first glance- it's using all the graphical whiz-bang of the highest-end systems (and more) to produce an experience that's reminiscent of a first-person shooter. WoW's graphics can't compare on the 'highest polygon count and most convincing reflections on water' score. But it more than makes up for that (in my opinion) with artistic merit- the design sensibility of EQ2 is, frankly, rather bland and ugly in comparison (judging from screenshots). The graphics in an MMO is important when you consider how much time you'll potentially spend staring at them, and no one's going to go blind from playing WoW.
I could go on and on. There's a well implemented PvP (player vs. player) and RvR (realm vs. realm) system right out of the box. EQ2 has no PvP whatsoever- not even duelling. WoW supports guilds and raids, which is expected from any MMO. There is almost no zoning whatsoever- only when entering "instanced" (that is, private) dungeons and one or two other places do you see a "Loading" screen. WoW has the best travel system I've ever seen, including flying creatures (gryphons for the Alliance) that literally fly you through the world at about 5 times running speed. It's akin to flying in a helicopter- you see people running around, battling or just chilling, below you. You see areas that are 20 or 40 levels beyond you. You fly right over the mountains between areas and get a whole new view of the world- all without a loading screen. Even TRAVELLING is interesting in WoW.
I'm picking up my copy on the 23rd, and I plan on playing this game for a very long time. It's what you expect from a Blizzard game- a familiar concept polished and perfected. Get into it.