A short spoiler free summary on the SP.
Time played: Around 4 hours
Sound: Best thing since sliced bread. The sound is seriously good. Insanely good. Easily the best I've heard in a game. Guns are immensely satisfying to fire, gun fights sound awesome and the various environments sound exactly how you would expect them to sound should you be there. Take it from me, it's that good.
AI: I'm in two minds over this. Sometimes I would blow up an area and they would stand around completely disinterested, when at other times they would stalk me like lions stalk a gazelle. The squad AI is actually very good, they would kill 20-30% of a group of enemies and then leave you to pick of the rest. There is various parts in the game I needed them to save my ass and they did so. So in short, squad AI very able, enemy AI is a bit unstable (at times).
Graphics :Almost rank up there with Crysis, seriously. Draw distance is marvellous, character details are fantastic, smoke effects, destroyed buildings, environment and vehicles are just grand. My only major complaint is the bloom effect which will freaking blind you at times. It does get so bad at a certain point in the game (a car chase) that it becomes close to unplayable. I did try and fiddle with the settings but sadly it remains a major problem.
Difficulty : This will differ from person to person, and might irk all the FPS gods we have on this forum when I say the difficulty is somewhat ... difficult. If you don't play your games on the hardest setting, you're doing yourself an injustice. Hardest setting on this game would keep most people busy a long time and not quite allow you a run and gun game as doing so would kill you pretty quick. So, difficulty levels, perfect.
Gameplay: I like it. I like it a lot. Ever changing environments, innovate game play (one tiniest of spoiler ... fire to fire), various type missions and a sound overall story. This doesn't do anything brand new but what it does, it does well. I never felt like I had to play the same type environment twice after four hours in already. Again, I like it.
Story and Dialogue :The overall story, while not something never done before, is rather able. It make sense at all times and is acted out in a way that's easy to follow. Most of us that play these type of games don't care about the story and just like to blow **** up, but here you can't help to pay some attention to it.
The game dialogue between your squad is awesome. Slagging each other off, a lot of swearing, heaps of sarcasm and irony and a healthy amount of disrespect for authority. They act and talk exactly what I expect these squads to talk like. You would love it.
Overall verdict : a solid 8/10 for the single player.
I'm not a professional game reviewer so cut me some slack. I just quickly threw this together since there's already a lot of negativity surrounding this game with the majority of people not having even played it.