I imagine the backlash from fans of the respective franchises will be a lot worse than Paul W.S. Anderson's original PG-13 flick. The first one was mediocre and painfully safe; it totally wasted the characters, but save for some continuity errors with the Alien canon, it really didn't offend anyone. This one is dark and mean, takes massive liberties with both franchises and churns out something that really hasn't seen the light of day in this decade or the last one. But I'd rather see something like this, which is entertaining at least on one level, then something that is basically censored fan fiction filmed by a barely competent director.
My guess is that fans will detest this installment and clamor for a return to each series' roots, but the problem is that just cannot be done within these crossover films. We're essentially dealing with comic book movies, complete with all their faults, and you're not going to be able to replicate what made the original films so great in dealing with the material like this. But - fuck it! - if you're going to have monsters duke it out, do cool shit like this. Make it Grade-B. It's better than it deserves to be.