I liked Y Tu Mama Tambien much more than I liked Children of Men. The latter I just didn't think was so special. The story is hackneyed with a couple of annoying holes (the mysterious deus ex machine of the Human Project and the silliness of one baby making all the difference: there'd have to be mass fertility for the tide to be turned in humanity's favor), the metaphor heavy-handed, the acting acceptable but nuttin' special. Michael Caine's character was a caricature, however likable. Owen's was a stereotype. The whole thing, in fact, was a cliché--well-done and reasonably interesting/entertaining but a cliché nonetheless. The action, I grant you, was done well, but I think it should take more than snazzy action sequences to earn four stars.
I call Emperor's New Clothes.