This movie blew and it got the proper treatment from moviegoers. Simple as that. They could have made this an EPIC movie, the Matrix of this decade, but they blew it.
I agree it should have been more epic, but I don't think if would have made much of a difference with moviegoers. The trailers were already putting most of the emphasis on the alien/outer space stuff, and people still weren't much interested.
I think it probably looked more like a scifi film aimed at nerdy 14 year olds than the kind of mass appeal superhero movie people are used to seeing.