It's actually a clever concept. Setting aside the atrocious movie made a couple years ago, there have actually been a few genuinely good AvP stories.
The original Dark Horse comic tops it all, of course, and it deserves most of the credit for the clever concept of the series. Basically, the Predators are a race of hunters who like to hunt challenging and dangerous game. Now, the Alien is indeed a challenging opponent, so the ever-resourceful Predators actually manage to capture an Alien queen. They lock it up and restrain it, but the also force it to lay eggs. Each egg is inspected, and if the egg contains another Alien queen, that egg is destroyed. Regular alien eggs are then put onto small spaceship probes which are then sent out to habitable planets - sorta like they're stocking the planets with game (and since there's no queens, there's finite number of prey). Predator hunting expeditions then go out to the stocked planet and hunt the Aliens. Again, the Aliens are dangerous, so it's not unheard of for a Predator to lose it's life in the process - but usually the group of Predators still emerge victorious. Now, the comic books up the ante a little. The Alien queen isn't completely helpless, it seems, and manages to trick the automated Predator machinery into allowing an Alien queen egg to be sent out. Of course, those eggs are sent to a planet that also contains... humans! The series goes into some detail on the social habits of Predators, and even manage to establish an individual Predator (who has a chipped mandible) character that we can relate to (he's an honorable guy) and some humans that we care about as well. In the end, the story worked really well, and lots of other projects were kicked off.
The original comic book series was followed by a slew of other Predator crossovers: Batman versus Predator, Superman vs. Predator, and Aliens vs. Predator vs. The Terminator (of course!) are just a few examples. Naturally, none of those series captured the imagination of audiences quite as much as the original. The clever thing about AvP was that the Alien just fits much better into the role of prey, and the writers were able to play around with that concept in new and interesting ways. I've only read the Batman vs. Predator series (which was mildly lame), but it seems like all the other Predator spinoffs were basically reliant on the same premise: Predator wants to hunt something challenging, and Superman/Batman/Judge Dredd/whoever is much deadlier than your average human.
There was a series of video games based on the AvP universe. I've only ever played Aliens versus Predator 2, but it was a great first person shooter - among the tensest games I've played, it constantly had me on the edge of my seet or jumping as an Alien pounces. You also get to play the game as a human, Predator, or Alien, and the game's story (which isn't anything special, but not actively bad either, and playing from different perspectives is actually pretty cool, because you get to fill in some of the blanks). The video games capture the feel of the AvP universe and create a wonderful sense of atmosphere (when you're the Colonial Marine, for instance, you've got the motion tracker pinging away at you, which can be just excruciating at times). The games are quite effective.
A pretty good movie script which basically adapts the AvP comic series was written, but apparently shelved in favor of this crap. This really baffled me at the time (and I guess it still does). I know, I know, what was I expecting? "Versus" movies don't exactly have a high quality ratio and so most people expected dumb action (which the movie barely manages to deliver). Indeed, when I recently saw the Hitman movie, I had appropriately low expectations for the film and was thus not dissapointed (incidentally, that movie was much better than the first AvP movie, which, granted, isn't saying much, but still). However, the Hitman movie was based off a series of video games that had no real plot (you play a hitman who must, you know, kill people), so it would make sense for the movie to be complete crap. AvP, on the other hand, had compelling source material with a proven track record. Not only that, but comic books are notably easier to adapt than literature or video games. The biggest issue with adapting a comic book is knowing which story arc to pick, but AvP was a 4 issue series (i.e. it's not like Spider Man, which has been churning out story after story for decades) so that problem is non-existant. So, to recap, you've got compelling source material with a proven track record that will be really easy to adapt (heck, the comic books are basically a set of storyboards!). I suppose you could be worried that the comic book audience would be bored by a simple rehashing of the original story (which I don't agree with), but you've got to realize that the audience for a new Aliens or Predator movie is much larger than the audience of the comic book ever could be.
So whatever, the filmmakers decide to go another route. Fine. So what do they do? The change the setting to be the polar ice caps of Earth, put a Predator pyramid under all the ice, and put the whole Alien queen contraption in that pyramid. They somehow feel the need to tie this movie in with the Alien series by employing the services of Lance Henriksen (who is not playing an android, but rather the human that the android is based on), but then they get crap talent for everything else. It's just an awful, awful movie. I've already rambled enough, so I won't bore you with all the things this movie gets wrong, but I do want to call out one thing: the Predators are absolute wimps in this movie. In the comic, the Aliens get the better of most of the Predator hunting party, but only because of sheer numbers (because there was an Alien queen on the planet, there were way more Aliens running around than expected). And even then, you've got Broken Tusk (the good guy Predator), who's just an absolute badass and manages just fine despite the numerical disadvantage (with a little help from a human). I dunno, maybe people like the Aliens enough that they want to see them win all the time, but personally, I can relate much more to the Predators. They at least have some concept of honor and personality, and I enjoyed seeing them team up with the humans in the AvP comic books. I mean, they've got the technology, the smarts, and they've obviously been hunting Aliens for a very long time, so why does the movie consistently portray the Predator as being a helpless weenie when faced with even just a single Alien? I really don't get it.
Aliens vs. Predator: Requiem just came out yesterday, and from initial reports, it seems that the new movie is just as bad as if not worse than the original. How this is possible, I do not know. Do I have the guts to actually find out? I'm not sure. I'm usually up for bad movies like this, but I just don't know if I can take another round of this crap.