It doesn't actually look that bad. Like a half decent action movie I guess.

I know the "how the monsters came to be" part is going to be different...but otherwise I don't understand how films like this are still getting made.

It DOES look reasonable but we've seen this film before. Aliens sprang to mind immediately but Resident Evil also needs a mention. I'm just recently watched Alien vs. Predator and the similarities (apart from backstory) are overwhelming. Crazy.