A perfect franchise match-up, as the ultimate "sport-hunter" takes aim at the the ultimate natural predator.
The film does an excellent job of merging the two legendary franchises, and even though it takes place in the present (long before any of the Alien movies), they do a great job of tieing it in to the series' continuity by having the main characters funded by Mr. Weyland, founder of Wayland Industries, better known as "The Company", the sinister organization that sent the Nostromo to capture the original Alien. This at last answers the question of how the company first found out about the killing machines.
If you are a fan of either series, I can't recommend this movie highly enough, and consider it the best of either franchise (though I have not yet seen AVP 2).