Is the 1986 movie Aliens much scarier than the 1979 movie Alien? I have seen Alien.
Alien is a horror film. It should be scary as it is essentially a haunted house in space. The movie Aliens on the other hand is a straight up sci-fi action extravaganza. It is directed by Jim Cameron who cut his teeth making sci-fi action movies like the Terminator. There may be one or two intense scenes in there but nothing along the tenseness that was Alien.
It's way less scary than the original. Very enjoyable in its own right, though I have always resented they turned those mysterious creatures into ants, basically. But Mr. Cameron pulled it off brilliantly anyway. The only scare I got from Aliens when I watched it in the cinema was the (for its time) awesome sound effects. Made me jump a couple of times! I think it won the Oscar in that category, actually.
No, Aliens is an action movie. The enemy is the Aliens.
Alien is scarier than Aliens, just like Terminator is scarier than its sequel.
In both franchises, the first is a small scale, scary horror-scifi, while the second is a larger-scale action-scifi movie based on it.
And all four movies are fucking amazing!