Different styles. Cameron made an action movie. The first movie was more of a horror movie with a little sci fi thrown in. Cameron’s (second) movie was a bit too campy.
Ridley’s Alien was NOT campy.
I found Alien an empty-headed horror movie with little to recommend it beyond the disco-inspired art direction and some gimmicky cinematography. The suspense techniques looked tired in the 30s: for the most part, things simply jump out and go “boo!” Under the circumstances, the allusions to Joseph Conrad (Nostromo) and Howard Hawks (The Thing) seemed rather presumptuous.