I've been a very on and off comic reader for about 30 years and one thing I notice from taking months at a time away from comics is that many times when a villain gets popular
Marvel allows them to be interchangeably used as a hero or anti-hero or villain. I have often been surprized to come back to reading and find my favorite villains no longer villains. Some of those surprizes have been Punisher, Rogue, Sabertooth, Marrow, Stacy X, Thorrn, Feral, Jack of Hearts, Absorbing Man, Sandman, Black Cat, Electra, Mystique, Quicksilver, Scarlet Witch, Black Widow, Atlas, Gambit, Kaine, Grizzly, High Evolutionary, Puma, and of course Namor has been just about everything in his time. If you change all the bad guys into not so bad guys, you get left with all second stringers.
Given my selective reading of late... I'm sure some of these guys are dead or heroes or something, but I'd like to see more of Steel Serpent, Master Kahn, Moses Magnum, Bullseye, Kaine, Grizzly, Mole Man, Mad Thinker, Puppet Master, Bushmaster, Purple Man, Quasimoto, Selene, Taskmaster, Tatterdemalion as bad guys.