Reaver's the guy you love to hate. He's an infuriatingly charismatic prick who you really want to see get his long deserved comeuppance, but at the same time he adds something vital to Fable 2 & 3; an anti-hero who is running on his own agenda, and no-one else's. Reaver does everything he does for no-one other than him, and that's why he works so well.
There's no darkness to make him make cruel choices like Logan. There's no tragic family death like Lucien. He's just a smug twat who sacrificed Oakvale to escape the only thing he feared, death itself.
I don't think Reaver is evil, in all honesty. That's far too strong a word for him. He's pretty damn far from good too, for that matter. He's just.. well, Reaver.
I think it would have been awesome to fight him, but I don't agree with killing him. He adds something far too strong to the Fable series to just off him like that.