I don't disagree with what's been posted thus far.
I have maybe a few others to add...
Ghost Rider...the ability to defeat anyone by using their own memories and mind is brilliant and bitchmade OP.
That one woman who could make a black hole inside peoples' minds.
Possibly Solar from Valiant...by accident brought down the whole universe and all of existence to one singularity and himself...and had to live eternally to rebuild it all. So essentially became God. Though I will say he didn't quite do it perfectly and some nasty undesirable concomitants resulted directly. And he ended up kind of weak by the time he had remade all of existence like it was before. Just enough power to fight off the abominations created from his mistakes. So maybe he isn't OP...but still to pretty much become God even for just awhile......