It all depends on your definition of "serious". I've seen what happens when comic book films are dour and serious. They are cheerless, tedious bores, like Zack Snyder films. Captain America: Civil War has plenty of laughs, but that's about as serious as any Marvel film should get, although Nolan's Batman films have special dispensation to be darker, just because (and at least they have some humour for counterpoint). Given the choices between Snyder purgatory and a somewhat tonally inconsistent Thor film, I know which I'd pick.

Besides, I don't think the humour is as out of place as you and others have claimed. The ultimate end of the Natalie Portman subplot wasn't ducked, and I thought the humour provided a good counterpoint rather than being tonally misguided. Is the film brilliant? No, but it works well enough, in my not remotely humble opinion. In fairness though, I haven't read the comics.

Good piece regardless. :)