Fantastic 4 is just about what you'd expect out of any 3rd person brawler; there's enemies to beat, easy puzzles to solve, and, well, that's about it. You've no doubt played this game many times before, just never with the Fantastic 4 license.
That's not to say it's not executed well, because it all works out just fine, but it can be a chore to slog through the missions since they do suffer from repetition and stagnant level design. Some of the repetition is alleviated by the differing ways each character plays out (ie: the Thing is your big melee brawler, while Sue Storm has more stealth leanings, and Johnny Storm is quick if not powerful), but nothing really cures the debilitating problem of the often mediocre 3D brawler gameplay.
And if you're looking for eye candy, then the best you're going to get in Fantastic 4 is the picture of Jessica Alba on the box art, because aside from that Fantastic 4 is a pretty average looking game. The environmental detail is very, very bland, with the same going for the often blocky character models.
Fantastic 4 doesn't do anything atrociously bad, but unlike it's namesake, it never does anything fantastically well either. It's all merely mediocre beat-em-up gameplay with a license slapped over it. True believers, and just about anyone else, would do best to just give it a rental.