Not only is this game the best mmorpg I have ever played, but it is one of the best games ever.
Gameplay-
This game never gets old. Each quest is different and has great rewards. Not only is each quest different, but each one is just plain fun to do. The really cool thing though, is that, you never have to do any quests at all (though it is the best way to level up, and in my mind, the most fun). You can do so much more like explore or work on a profession (for example collecting plants and making potions or skinning animals to make cloths and armor). You could even do all of these at once, which I think is the best way to do so.
Graphics-
Maybe this game doesn't have the high polygons and the high-res textures, but what it does have is the best art that I have ever seen in any game. The art definitely makes up for the lack of high-tech uses like bumpmaping. The graphic style is just so amazing that it simply makes the world come alive. Plus, every environment is different, and the amazing thing is that just when you've been in one place too long and it gets old, you are able to move on (because of your character leveling up) to a completely new area. But the most amazing thing about the graphics is that, it is in a way that there are no loading times (except for when you first start the game and when you are going to switch continents). And even then, it takes only a couple of minutes if not seconds.
Sound-
The music in this game is brilliant. It fits the world so well, and it never gets old, because its not the type of music thats in a way in which it is annoying, it is the sort of music thats on the side. You're never really aware of it, but when you are, you will definitely appreciate it. The only complaint you might have that actually never annoyed me and I don't really care about, is that there aren't a lot of voice-overs for npc's.
Value-
With so many different things to do, and so many places to explore, you could be playing this game for hundreds of hours. And with blizzard adding new content to the game every month, I don't think anyone will ever run out of things to do in the World of Azeroth.
Tilt-
Everything just works and fits together so well, that you will feel like your actually in Azeroth as an Elf, Dwarf, Orc or which ever of the eight races your playing as, doing quests or whatever of the hundreds of things you could be doing.
If you don't like the idea of paying 15 dollars a month, wait till you play this game. I know that, before playing this game, I hated the idea of paying each month, but when I started playing World of Warcraft, that changed. And if your not sure if you'll like the game, just go ahead and try the 10 day trail, I'm sure you'll fall in love with the world of warcraft, Azeroth.
P.S. I highly recommend reading Greg's review, which is MUCH more detailed and better than mine.