I have played 90%r of all free games, and pretty much all P2P games. The reason why wow is the 800 lb gorrilla of the MMO world is because they took the time to design a world that entices players and keeps them active. It's a world where your interactions are viewed by other players and feels fluid and natural when your playing.
The graphics? This is often debated by many people when it boils down to it, doesn't matter at all. Wow has great graphics in my oppinion and I love the visuals. The details to each character, how the tails movve on your tauren when you run, the trees sway in the wind, it's the simple fact that they just don't have objects sitting there feeling processed and generated, but feel lifelike and animated. The world is huge and detailed. Wow doesn't feel like a generic program or have that bland lifeless feel, it feels like a game.
Now wow in my oppinion, has the best leveling system with constantly interacts with the world with unique quest and demanding chain quest that require people to treat this like a game instead of some random mmo which has you pretty much kill and repeat. In wow you do get those numbered kill quest, but atleast they have 100's of other quest that are truely unique to the game and keeps it balanced between questing and doing everything else that moves you.
And to continue on the questing. You can quest all the way to lv70. Uhh win? From what I've seen, games that force you to grind don't require much skill and or will to do so. You logon, kill 400 mobs, log off. Where is the fun in that? Now in all games you do get both types who do succeed at doing it,a dnt hose who fail as in wow, but I see it as, I would rather do a difficult quest requiring 5 people to do in 20 minutes then grind on mobs for 3 hours to get the same amount of exp. Loosing exp when you die? Last time I check, if someone teaches you something, and you get shot in the leg, when you get out of the hospital your going to forget that? Chances are no, so why when I die I loose exp when I die? To me, that is the greatest revolution in game not to be forced to regain exp when I die just to make me grind even more.
Class and skills are unique to wow and highlight each classes attributes and playing styles. Although they didn't really reinvent the classes, they did promote their skills. More balanced PvP then most games, rewards for pvp, and pvp games. To me thats a win because I've pvped in other games and tried there pvp deals and wow just has a great feel to it. AV being the only thing Alliance can win for some reason is my favorite because it gives a large scale group the ability to play together.
Weapons, armor, and accessories can be sumed up in a few words. PvP, raid, or make it yourself. Simple as that. And not like other games where you can just buy it from someone else if you sold enough cash shop items, or farmed a boss that gives you drops you can sell for alot. PvP rewards are great for those who don't like raiding but love pounding on people. Which is a good idea that just b/c you raid and I don't like to doesn't mean I shouldn't loose out on armor/weapons because you did something I didn't. Making it yourself is a great way to get yourself some really good armor and to make money.
Now wow isn't for everyone and this is just my oppinion. But I'd take wow over any other game because it feels like a real game to me. Idk if it's just me, but I'd love to see wow on next gen consoles with toons of next gen content. There are lots of things wow is still missing, but it's still got more than any other game I've seen. I'd love to see great things come to wow and me, I'm not even into the lore nor has ever played, read or viewed anything pertaining to warcraft before wow so that proves they can make a believer out of anyone. Lets hope in the future they keep it up, and would probably just need more cowbell.