WFRP was my first RPG book I ever owned. Now I own my third rulebook of this game (previous two were annihillated during the extensive usage, mostly due to poor binding of the book). And after almost nineteen years in the hobby, I think it's my favourite one (sorry CoC...). Here's why.
1. Evocative artwork. Some role-playing have outstanding images. WFRP hasn't - of course there are lots of amazing pieces of art there but some are just plain disgusting. But still - I'm not sure if there are more games with *that* kind of artwork - sometimes it's enough to look at one image and poof! Whole scenario materializes inside of your head.
2. Exciting character creation. Lots of side skills, shitty professions, randomly determined character age which has impact on amount of starting skills. It's always fun.
3. As I mentioned above - fuckloads of (sometimes) shitty professions. It's really amazing when you watch your character's transformation from the rat catcher or apothecary into an actual hero. And - if you are a GM - that facial expression of the player when he rolled up some pretty amazing stats and hit a servant or other (seemingly) useless and un-playable fucker.
4. Strange monsters. 2nd edition is full of well-organized and rather logically designed monsters, mostly derived from the WFB. What about giant leeches, carnivorous snappers and other strange inventions of the game designers?* AND FIMIR. AND ZOAT. Fuck yeah.
5. Setting. It's not said that all magic comes from the Chaos. Magic is magic, its background is irrelevant. Emperor is an old and demented guy (and they slay him during The Enemy Within campaign, which I love), World is not ruined. There is no shitty Archaon or other major pawn of the Ruinous Powers. Game world is not 100% based on the Fantasy Battle. AND FIMIR. AND ZOAT.
6. Adventure books. I played several 2e adventures and I ran more than several 1e adventures. They can't be compared. 2e adventures are just plain retarded, to the point of unplayability without some serious tweaks. And once again - dat artwork :D
*) of course I may be wrong, as I'm not an expert of the 2nd edition. In fact, I think it sucks, especially it's setting. Gods, I hate it.