Outright Villainy said:
I only have Corruption, and I thought it was pretty solid, if a little unspectacular. Some bosses are pretty cheap on the harder difficulties too, when you're forced to dump your shields into your guns to attack them, which gets insanely frustrating. It's a pretty good game though!
I, too, have only played Corruption. Now I kinda wish I would've just waited for this, but Corruption was still a great standalone game. I've heard positive things about the second, too, so your enjoyment should last, throughout.
EDIT: Oh, but unfortunately, I've heard that the first is the best, so you may be enjoying it most now. However, it's all personal opinion, so maybe the people I've heard that from were dead wrong.