Personally, I find Aliens to be rather boring. The build-up to the fight sequences is good, but the pay off is nothing more than a bunch of soldiers just shooting randomly. Guess what? Shooting randomly is not exciting or entertaining. I will admit that the characters are set-up very nicely, and I can appreciate that. However, most of them come off as jerks, so I'm glad to see a good chunk of them die.
I find Alien to be a MUCH better film, in terms of both action and suspense, as well as creating likable characters. Aliens has some elements that I enjoy, but when it comes to action, its nothing special.