Even if RE4 had a lot of enemy types, it didn't feel like it when nearly every encounter was filled with those shambling farmers or cult people. I don't know if Revelations has more or less, but encounters in that game felt a lot more varied simply because enemies were constantly switched up, for example. I still like RE4 way more than that game, though.
Anyway, I've only done Ch. 1 and 2 for all three campaigns so far (in Leon's Ch. 2 right now) and still don't know where RE6 is on my list. I like RE5 more than REV, I think, and really enjoy a lot of the mechanics and enemies in RE6. The scenario design, pacing, and oddball ideas like QTEs and stealth crap just bring it down for me so far.
RE6 is fun but unpolished. I'd say the same about Dragon's Dogma, actually, and I adore that game. Maybe I should play RE4 and RE5 again right after RE6? I honestly wouldn't be surprised if I liked RE6 more because character control means a lot to me.