The big stupid bits in the first one include the XO sticking his fucking helmet directly in the path of an opening egg. There’s also the matter of the Captain and XO both being off-ship on the same mission. Then there’s the totally fucking off the Quarantine Protocols (I know, the Science Officer was in on that).
As for the Good Sequel, well, yes, that. I’d expect some sort of fixed crew on the Sulaco, with an actual O-5/O-6 type CO, and a separate Marine structure. A Navy ship really does work better with squids - one really needs a CO, an XO, a Chief Engineer and a Master of the Boat (Some sort of CPO or higher).
I also expected the marines to have a variety of munitions for their rifles, so that when they went into the fusion reactor cooling area, that they could switch away from the armor piercing stuff to something else, like percussion rounds, or Hell, Double-Aught shot shells.
Then there was the stupid idea of not sending enough marines, and then committing all of them in one mass in one excursion. Stupid, even for a brand new space platoon leader. And then we have the sergeant going along with it. Stupid, stupid, stupid. Send in a small, fast element. And if you must deny your people their munitions, at least scratch the mission and rapidly extract them.
There were also a large volume of Invincible Ripley Scenes, where Ripley should have been torn asunder by hordes of the alien warriors.
Then there’s the matter of the drop ship’s flight crew not securing their ship - you don’t leave the drop ship unsecured in a suspect zone. At a minimum, leave the ship idling, ramp up, ready to react. Stupid. And, at least have the courtesy of granting your flight officers warrant rank or better.
And don’t start me on the mysteriously variable alien acid blood, which, depending on the scene, either burned its way through multiple decks of the Nostromo, or did much less damage on human flesh.
Thing is, in the first two movies, one can explain away much of the stupidity as company sabotage in terms of specifically setting up the people on the ground to serve as either host to the aliens or as AlienChow.
The really unforgivably stupidly rancid nonsense only really kicked in the third and fourth “movies.”