The Sentry IMO is a waste. Cool concept that really doesn't make sense in the comics. He's all powerful yet never really does anything. Why?
I thought maybe he's Uatu in disguise? A way Uatu to involve himself on Earth. Maybe the Sentry is the personifcation of Uatu's urges to involve himself? Maybe Uatu fell in love with a woman and planned all of this? I can certainly see a metaphysical/religious aspect. Uatu was created with those ideas in mind. The relationship can take a God/Jesus take.
The "evil" part of the Sentry is so he doesn't use his powers. Maybe this is on purpose. A failsafe by Uatu so other powers in the universe (including other Watchers) don't suspect the Sentry of being what he is.
I just think this twist would make the character much more interesting.