They probably felt that it was all they could use to create 'buzz'. Subtlety doesn't really work in the blockbuster game, y'know...unless you're specifically trying to hide something in the actual story like with Super 8. And then....look at the film (GL). Did it really have very much to offer that wasn't generic, aside from its effects and the stuff on Oa?
THere were similar sentiments around Superman Returns...like the trailers showed too much, they were all too similar, etc. But then....look at the film. Aside from the two action sequences, what did it have aside from a lot of heartache and strained emotions? How the heck are you going to attract mass audiences to a Superman film with that?
Marketing does deserve its fair share of criticism here and there...but they can only work with what they've got. If you want to build up 'mystery' and intrigue...it REALY helps if the film itself has got a lot of it to the extent that marketing can use a lot of material without letting the cat out of the bag. But if the film doesn't have it, you can't really manufacture that in marketing without running out of ammo really soon.
So those who felt that marketing 'lied' to them...if you were them, and you knew you needed to hit big on opening wknd to have a chance of making money with this film....do you really think it would have been better off being more 'honest' about the movie? Advertising it to be a rather run-of-the mill superhero story with some wisecracks here and there and just a little bit of space/aliens? Granted, it can tick audiences off and create bad word of mouth if they feel duped....but in a way, maybe they thought that they'd make more money overall by dupe-ing the opening wknd crowd into seeing it, rather than boring them away from it....because one way or another, it'd be clear after it opened how generic, etc. the actual movie is, marketing or no marketing.
It's like a lawyer defending you in court....you bet your butt he'll try to make you out to be a saint, even if you're not....because his job is to win the case, not tailor your public persona for the next ten years or what have you.