Calling AvP2 a bad movie would not be fair. Oceans Twelve or Constantine were bad movies, and categorizing AvP2 together with such movies would be an insult for them.
If you watch an Action movie, you usually don’t expect an intellectual challenge or a good plot. But when I think about recent Action movies, i think of Bruckheimer/Bay, and they did set a certain standard.
AvP2 is nowhere near that standard. Most of the time you see black Aliens fighting the black Predator in the middle of the Night or in buildings with no light – reminds me a bit of the Transformers Movie, but much much worse. Combine that undefinable action with the non-existance of a plot and you got 8 wasted euros for the cinema.
To add insult to injury, you have a wanna-be love plot twist with some annoying stereotype-blond girl and two guys. However, this love story has a happy end, as the girl and the bad guy die. (Well, pretty much everyone dies at the end, but it was very satisfying to see the annoying people die before)
So here is my recommendation: Do not watch this movie. Ever. If you really wonder what Alien vs. Predator could be, here are my recommendations: