on a serious note...
This movie is going to be nothing more then a cheesy SF-action thing... I even wonder where they got the money to do such a lame thing...
I will watch it on tv, when there is nothing else on. But I know I'm so gonna laugh at it...
It's like putting Superman into a Lord of the rings movie...
EDIT: let me put it in other way:
I've no doubt the film is going to be entertaining. But...
For whom is this film? For the Alien-fans? I'm sure the true Alien-fans wont like it that another creator from a totaly inrelevant space/time/story invades their story-line... And vice versa! Predator fans won't like the idea of Aliens roaming their story line... Although! There was a small flash of an Alien skull in one of the Predator spaceships in the second movie. But as in many movies, such small winks are often placed to contribute to other great movies (or movies which the director liked)...
So, I think, many die-hard fans will not like the idea... Although they're gonna watch it out of curiousity I think...
This is only a movie adaptation from those all-time questions like Spiderman vs Superman... Godzilla vs King Kong... etc...
So, who will win? 20th Century Fox... (I hope... for them... If they can make the story believable for both groups of fans)