I still have not convinced my group to play WFRP, even though I love the system.
It's a very lethal, "realistic" (whatever that means), system, something of a mixture between D&D and Call of Cthulhu.
The world is kind of a "fantasy Europe", much like Ars Magica, but less connected with the real Europe.
It's a world that opposes Chaos to Law much more strongly than it opposes Evil and Good. In this, it can be compared a bit to the Planescape setting. But that's as far as it goes in relation to PS...
The system is fast and easy to learn, the advancement system (through "Careers") is much like the idea of Prestige Classes in 3E. Characters' power level can be roughly estimated by the number of careers the character has been through.
Wizards are very powerful, but take a longer time to get to that power level, due to the system of experience.
Some monsters are basically indestructible, but this can be easily understood if you grasp the concept behind the world.
In a nutshell, your D&D players may get the jitters with this one, but your Cthulhu players will have a LOT of fun.