Tell me about Matt Wagner's Grendel.

The only Grendel story I ever read was a crossover story with Batman. It was a lousy Batman story. I came away unimpressed with Grendel. Realistically, though, if it was the only Batman story I’d ever read, I would hve a low opinion of Batman.
Grendel has been around since the early 80’s and apparently there is a pretty solid fan base. So, tell me what’s so cool about Grendel?