I personally thought Rhino was done fairly well... for the 10 seconds we saw of him. He wasn't entirely stupid or crazy, and was a real threat, yet still was funny. That is... if you are reffering to in TASM.
I think cartoony is good, as long as it is done well. Heck, we wouldn't want a non cartoony spider-man would we? He wouldn't be as funny!
It's fine for them to be funny, and slightly unrealistic. I mean, IRL people would never waste breath to throw a few funny lines when fighting super-villains. But spidey is given a certain self confidence that allows him to do this in a slightly realistic way. Same can be done with villains.
And yes... I want a fishbowl.