Sequel Exceeds 1st Installment (List)

Agree on Spiderman 2 -- at least, the CGI was definitely better. I kind of got tired of Peter Parker getting crapped on from every direction. But it was still ultimately a better movie.

Don't know about Aliens being better than Alien -- they were just different. Alien was a horror film, Aliens was an action movie.

The Road Warrior (sequel to Mad Max) -- Mad Max was low budget fun, the Road Warrior was the movie they meant to make.

Ditto 'Desperado' (sequel to El Mariachi) -- a real sequel, but basically remaking the film with a real budget.

Batman Begins (prequel to the Batman franchise) -- just superb, easily the best of the entire franchise. It was a brilliant thought, whoever had it, to reimagine the entire history -- that's the sort of creativity I usually only see in books and graphic novels.

Star Trek 2: The Wrath of Khan (2nd installment in the Star Trek franchise) -- not saying much, the first movie was tepid, but the 2nd remains quite possibly the best of the old school franchise.

I can list a few movies whose sequels I thought were as good as the first:

T2 (sequel to Terminator) -- different budgets, not really comparable.
28 Weeks Later (sequel to 28 Days Later) -- completely different story, same great concept (zombies, sort of)
Toy Story 2 (sequel to Toy Story) -- they were both great.
Evil Dead/Evil Dead 2/Army of Darkness -- what, are you kidding me? Some of the greatest moment in celluloid are in these films.