For Cowboys Vs Aliens, you really, really must go into it with the right attitude: the title of the film sets the mood you must embrace. Really, it acts like a conventional (emphasis on convention) cowboy movie: big, too influential rancher who likes to throw his weight around (Ford) and mysterious Man With No Name who can kick almost anyone's butt and has A Past. Only, they work together to take down (there was no doubt, right? so it's not a spoiler) an even bigger enemy.
I think Ebert was right that this would have been a better film if it hadn't been aliens, but some other Outside Force. Still, I think that injecting the alien element set the tone they wanted: just something to sit back and enjoy, allow yourself to make all the comparisons you want to the Clint Eastwood films, but without the weight of trying to make everybody not compare it to John Ford's westerns.
Eye candy, sure, but not so in your face as to turn off men. In fact, as probably expected, most of the audience was male (and college aged--but this is a college town). My own 20 something kids scoff at the idea of this movie and hubby went to humor me.