I've finished the main story of LEGO Marvel Super Heroes, and as expected, it was as shallow as shallow could be. That's not a problem, though, because it was so damned charming that any pretensions of depth would have spoiled it.
In the end, the heroes and villains have to team up to stop Galactus, who is being controlled by Loki and made to devour the Earth (though I suspect he would have done so anyway). It is so cute, like seriously. There's a scene where they're all hanging out in the S.H.I.E.L.D. helicarrier's break room, playing games, and then suddenly a huge brawl breaks out, and it's pretty much everything you'd want from a kid's super hero story.
After Galactus is defeated, the villains are rewarded with a 30 second head start, which is both silly and dangerously irresponsible, but like I said in my previous post, the heroes and villains are more like rival sports teams than deadly enemies, so it fits in perfectly with the tone.
I guess all I have to do after this is various open world content, and going back into my previously played levels to try and find all the collectibles. On the surface, this sounds pretty dull, but given that each of the side missions so far has been a cute little joke, and the game's levels are filled a variety of side niches to explore and puzzles to solve, going after that elusive 100% completion is likely to be an amusing diversion.