Not as bad as people thinks.
Let's look at the problem people are talking about:
Alright, I can related to this, the graphic is very poor, textures has really low resolution, and no "Real" anti-aliasing options make things looks jaggy at times. But to say it's horrible? I'm sure you guys hasn't played FEAR 3 before, it's graphic is way worst than ACM, it's story is uninspired and makes no sense at all, but it scores 7.5 on gamespot, really? If we apply the standard people enforce on ACM, every game needs to have Crysis level graphics and big-shot writer script to be call a decent game. But since it's obviously we don't judge a game by it's graphics, than why does ACM gets so much more hate for this?
AI is stupid, no challenge unless play the hardest difficulty
I finished the game on Soldier difficulty, I don't even know where is this opinion coming from, the AI is fine in my opinion. Yes sometimes your AI teammates get stuck on some places, but it's not like it never happened to other games before, and for me it only happens 1~2 times so it didn't bothers me at all.
Enemy Xenomorph are fairly intelligent, I heard people are complaining about "They only charge at you, they don't flank you or anything." I have to say from my own experience, the xenos can move very fast and surround you very quickly if you don't have a good aim, also they pounce at you from a distance sometimes, makes you have to keep pressing E to survive, I say they are fairly challenging. Don't forget the Xenos outnumbering the player by a huge percentage, if they all play hide and seek and being very smart, marines won't have a chance! You wouldn't have a game here.
Story makes no sense, bad ending.
I partially agree with this, the game could use a better story, the ending is a bit abrupt yes, but understandable.(sort of) But even though, I don't think the story is THAT bad, not bad enough to warrant all the hate it got anyway.
Ultimately, I think it comes down to the mindset you got when you play the game. If you got all hyped up by the PR, then you probably going to be very disappointed. But when I play this game I walk into it with one simple mindset
"Kill Xenomorph with Pulse Rifle and Smartgun, visit Sulaco and LV-426, experience the scenes from the movie "
And I got everything I was paying for, so for me, this game rocks, as for people who expected more than this, unless RIDLEY SCOTT and JAMES CAMERON themselves are working on this project, you are expecting too much from Gearbox.