I've seen all the Alien series and frankly you can skip the first one.  The first one is more a horror film.  The second is much more science fiction oriented.   I think you're asking does the second film stand on its own and yes it does. 

You get enough back story with Sigourney Weaver's character to see that she's freaked that The Corporation wants to go back and check out the whole Alien thing and they send out the space Marines which is really a lot of fun. 

Write a review about Aliens at the Forbidden Planet community when you're done! (Shameless self promotion!)