If the original did not exist and the sequel were released today, it would be called the greatest summer popcorn flick of all-time (just look at the ludicrous reactions to Star Trek).
But as previously stated, the 1984 classic is pretty much perfect. Save for some rough special effects (most of which still look ten times better than crappy CG efforts), there's not much you can improve on. The writing is fantastic, pacing is wonderful, actors are on their top game, etc. It truly is an example of a production coming together to make something totally original.
The sequel suffers from being too family friendly (the tone of the original was much darker) and it pretty much is a remake of the sequel in terms of structure.