I don't really dislike the Sentry, but I just can't care about him. I blame the fact that he's a golem. It's been years since he first appeared and let's face it, he doesn't have a personality beyond being horribly strong and possibly insane except when he's not but he might be. Not that you'd know from him.
If Marvel just shunted him off to the side for a bit, gave him his own series, let him evolve on his own, I might like him. As it is, his sole reason for existing for the last almost four years is to stand around in the Avengers and do whatever the person currently leading the Avengers tells him to, be it Captain America, Tony Stark, or Norman Osborne.
Marvelman, well, he's got more personality development in 24 issues than Sentry's had in nine years. Same powers, essentially, but none of the character.