Aliens (2003 Director's Cut):
Aliens originally came out in 1986, which is just seven short years from Alien, the original film, but it might as well have been the fifty-seven years Ripley was asleep because that is how different these two films are.
As I said in the last post, Alien is a horror movie. It's dark and scary and creepy and did I mention scary. Aliens is an action movie. It's got space marines  and they have lots and lots of firepower. This isn't seven people stuck on a spaceship trying to hide from the monster. This is a straight up war between the good guys and the bad.
Really everything you need to know can be seen in the two opening titles. In Alien, there is a painstakingly slow crawl across space during which bits of something slowly, oh so slowly appear. Until finally it's all there and you see the title, ALIEN. 
In Aliens, there is some fuzzy blue light and then very quickly it resolves in the title, ALIENS. But the whole thing is done in 1/20th the time. 
Don't get me wrong, I like this movie a lot. In fact, I've seen it many more times than the first one. Probably in part because they show it on TV much more often, but also because it is more fun to watch. It's not scary, scary boogums. It's guns and explosions.
A big part of the difference in the movies is just the number of aliens. In the first movie there is one alien. You never get to see it clearly. It could be anywhere. It's terrifying. In the second movie, there are hundreds of the aliens. You see them, if not clearly, more clearly. And while they are everywhere, they are just the "bad guys" of the film. They don't really have any more power or coolness then any other nasty from any other us verses them film. 
The special effects in the second movie are also worlds better. Many advances were made in the seven years between the two films. The spaceship shots, while still clearly models in some shots, most of the time look great. The computers and technology in the world and on the ships, while still not "modern" looking are much better than the TRS-80's  the first movie was using.
Even the painful fake head from the first movie is improved upon. Granted in this movie there is half android  but it looks so much better.
In watching this Director's Cut, I could definitely see where things were added. Most of it was fine and I liked the addition. However, the early scenes with the colonists find the space ship and such were really not needed and took away from the whole.
Don't get me wrong, I'm not saying the movie doesn't have its tension but it's just not the horror movie creepiness of the original. Which is fine by me.
Also, while it's way crueler than my statement about leaving the cat behind in Alien. Sorry Newt, but if it was me, there's no way I'm going down into that nest to get you.
 - And that should tell you everything you need to know.
 - Just like the movie. There's something out there. What is it? Can you see it? Oh dear god!
 - Just like this movie. There's something wrong! It's Aliens. Let's start shooting.
 - Don't get me wrong, they still bleed acid and can bite your brain out of your skull, but in the end that's no different than bad soldiers who throw grenades and fire machine guns. Either way you are dead.
 - Or is that too obscure a reference?
 - Sorry, artificial human.
 - I mentioned this in the Alien post, but I didn't see a clean way to talk about it in this one. So here's a long footnote. Aliens was the first rated R movie that I ever saw in the theater. It came out before April in 1986. I know this because I was only 15 when I saw it and I turned 16 in April of that year. I had not yet seen the original and I went with my older brother and a friend of his. I had no idea what to expect. Anyway, the funny part of the story is that we all bought our tickets separately. My older brother, who is six years older got carded to get into the movie. They didn't ask me for ID at all.