I'm glad to see Aliens & Terminator 2 on here because those were two of the best sequels ever made, period. Dark Knight came pretty close, but seriously, anyone who disagrees on this either dislikes action movies, or grew up in the 2000's raised on ADHD inducing special effects movies and terribly cliche dialogue. If you don't fall into any of these two catagories, then you need to rent them now before you begin to argue.
Actually I just watched Aliens, the special edition, a few nights ago and I'm amazed to see that it's still just as kick ass as I remember it was 10 years ago. It's rare for a movie these days to have such well written dialogue and deep thought that goes into the action. Who cares about all the special effects with CGI these days, Aliens and T2 pulled off their epic stories in 1986 and 1991 respectively, with limited special effects technology, but their amazing attention to character development and action earned them millions of fans as a result.
Directors today really need to analyze why the old movies were so good in the first place before they continue to screw up the new movies, like Terminator 4. There are too many new movies and sequels today that are just special effect borefests.