Warhammer kicks so much ass, that ass's ass is itself pre-kicked before it's even born.
Warhammer is cool because it has more gruesome kickass art than other rpgs. If all the art from all the rpgs got together and had a big fight, the art from Warhammer would win because it has big robots and monsters the size of entire buildings or cities in it, and they would crush the art from other games under their treads. Warhammer art conveys the feel of an entire world whose ass has been kicked. It has things that will sex you up while they tear open your body and soul. IN THE ART.
Warhammer is best for roleplayers who understand that you often better run away, and if you're lucky you'll just mutate and go insane while losing a couple of limbs. It might not sound like fun, but if you're playing Warhammer, it's all about the sheer magnitude of things. Chaos is fated to win; you're fighting a hopeless struggle; well stop whining and KICK SOME ASS. Even if just by running away!
Warhammer is cool because whenever you think you've managed to save an innocent, prevent horrors, root out an evil cult or whatever, you've actually set off a chain of events that results in your being blamed for the murder of the local high-ups, an invasion of beastmen, the collapse of the local economy and the loosing of a plague in a metropolis. Meanwhile, the innocent that you rescued gives birth to some kind of demonic spaceship that shoots pure pain from its giant cannons and launches a salvo of attacks that kills your descendants for the next ten generations.
Oh, and Warhammer is cool because it has the most skulls of all.