KMFDM is an older group, when I listened to them back in the day they were kind of an industrial band, really heavy.
Ill Nino is a heavy band. Pretty hard from what I hear, haven't had a chance to hear them yet.
Slayer is some old school death metal. They rock, period.
As for the other two, my mom told me "If you don't have anything nice to say, don't say anything at all."
Oof, you beat me to it, sorry to re-post most of the same stuff. I would call Ill-Nino Thrash metal or something like it.