I thought Ener looked like Eminem before I learned that Oda likes him.
But as for the topic at hand: Mayuri from Bleach. He does the mad scientist thing a lot better than Szayel, plus is less of an outrageous faggot.
Agreed, particularly after watching his fight in the dub. Mayuri has so many ways to kill or disable you it isn't funny…its just shonen circumstances that Ishida was even able to pretty much nullify him. (but its probably my favorite Bleach fight of what I've seen...though the Ichigo/Ikkaku and Ichigo/Kenpatchi ones are good too)
When it comes to OP, though, I really don't know who's that underrated. Probably say Wapol (though someone else already did), but I think Gin is pretty underrated as well...not to mention his battle hammers are just a cool weapon. Kumadori could fall in that category too due to how easy Chopper destroyed him...but before Monster Point, he was just a beast in revival.