I did a quick playthrough of the game with V4.5 of the mod. Note that when I reinstalled the game I did not play vanilla at all and so have poor memory of how the game is without the mod. Played on Ultimate Badass. Started with the No Changes difficulty but put on tougher soldiers for later missions.
The higher Alien speed made the game more enjoyable for me since I found myself looking around more often. Many times I would turn around, see nothing, then turn again to see an Alien in my face. Very pleasant. Sections where Aliens can spawn to your side and behind you are the best. The late game is really bad, since the Aliens always just rush you from the front, and even with the changes still attack in a straight line.
In indoor sections the Aliens were more fun to fight. I'm not sure if it's shit pathing or what, but sometimes Aliens would just run right past me, towards my side. This was not a bad thing, since it actually gave his buddies a chance to run at me from what used to be my front. I would see Aliens jump into spawn locations when shot at and then reappear later. Coupled with multiple Aliens it creates the illusion that they are flanking you and distracting you for their siblings. Sometimes they seemed to "bug" out and just stand right in front of me on all fours. Most of the time this looked pretty stupid, which is unfortunate, but I can recall at least one time where one did it among lots of dead bodies, and I actually thought he was dead. I walked almost right into him before noticing his tail wagging. Was pleasantly surprised. I still think they can afford to be even stronger.
I thought Lurkers could also have used a speed boost. I found them pretty lacking in general, and only ever died to one in the warehouse where 3 appear. It was actually pretty neat. One attacked me from the front while his friend pounced from the side and killed me. They don't usually behave like this. The locations they hide in are obvious and they are really slow when compared to the soldiers.
PMCs continue to be the worst parts of the game, but I have some memory that they were way worse in the vanilla game. Only one segment with them gave me cancer and that's when you have to leave the Sulaco on the dropship. Mostly thanks to random pin-point accurate grenades that they'd throw from the floor level onto the catwalk.
It is still very irritating that the guns in this game are inaccurate as hell beyond 10 meters. The assault rifle's stupid scope attachment is completely worthless because the gun shoots wherever the f**k it wants. I think it was like this in vanilla as well. You'd spend a clip shooting a stupid PMC because your asshole marine can't shoot straight.
Melee is massively overpowered and I'm not sure what can be done about it. Although the Aliens would get surprise slaps on me my elbow would bail me out easily every time. Coupled with the guns killing so quickly at close range you'd need situations where Aliens attack from multiple angles, but these are rare.
I was divided on how AI teammates work. It's good that they are useful, but they trivialize some encounters. They saved my ass loads of times but it made the game a bit too easy. Also, my teammates killed the Crusher literally instantly. He charged at me, ran past me and into my friends, and Cruz just executed the motherf**ker in one shot.
All in all, I am impressed with what was done. The game is elevated from a piece of shit to a game firmly entrenched in mediocrity with some highlights. Nothing can be done about the story or the missions being interactive cutscenes where you move in a straight line for 7 hours but the gameplay itself feels improved. Hudson's rifle is the actual pulse rifle, full auto and all. Why they made it burst fire only in the first place I'll never know.
I didn't play vanilla to compare but the game seemed darker and more foreboding than I remember, which are positive qualities. I also think I had a harder time telling dead Boilers from living ones, which I recall stuck out like sore thumbs to me on the vanilla game. Maybe just misremembering.
Edit: I forgot to talk about acid blood, which goes to how just how little it does. I think I read that it does deal more damage but I'll be damned if I noticed. As far as I was concerned, the acid blood did next to nothing.