Just finished the SP campaigns.
I dunno where some people are getting it from but the graphics are amazing. I'm playing on medium settings (If I play on high graphics I lag in open areas) and extra is too much, even indoors.
And already on medium graphics settings it looks absolutely amazing.
The SP campaigns aren't that short either. The Marine missions are a bit like Doom. Very dark, and every time you hear the little beep on your heartbeat monitor you're looking all around you. Playing ot on Nightmare now which has no continues (So if you die, you gotta completely restart the mission you're on) and it's a true bitch. If you aim to finish it on the highest difficulty setting just compare it to CoD veteran difficulty (Which is actually easy compared to Nightmare, lol).
Predator and alien missions are all about stealth, picking your enemies off 1 by 1. Doesn't work with Aliens though, they can see through stealth and attack in waves.
Alien missions are more about finding your way through shafts and whatnot else, and is also about stealth.
The AI is indeed not that clever.
The finishing moves and stealth moves are absolutely brutal. The first time I've seen some I was like holy shit! There are only movies from MP on youtube as far as I can see, but it looks a lot better in SP.
Predator for example picks someone from behind and slits his throat with his blade. Another one is that he thrusts his blade through the back and you see the blades coming out of the chest.
Aliens do the same but with their tail, piercing right through them. They can also chop off heads with their tails and ofcourse the populair headbite
The MP is still lacking though. Waiting for dedicated servers atm since the match making sucks. But the gamemodes in itself are ok.
) and I hope that the MP is fun. I personally enjoyed the demo. Think I just like the feeling of something creeping up to me as a Marine and then shooting the crap out of the Aliens 
