I thought it was a great game. Unfortunately, I never understood the whole hysteria about it being really emotional, mindbending and whatnot. I'd like to write a tldr post but I see a few people have already done that already, so here's a condensed version:

OLD MANUS PRESENTS MGS4 IS A GREAT GAME, BUT:
  • The script is godawful. It's like watching a direct-to-video 5th sequel of Shark Attack. Snake's rousing speech to Raiden at the beginning of Act 4 or something, on the helicopter, was so heavy with cheese it was a surprise the characters didn't suddenly don berets and start conversing in french.
  • Snake's voice in MGS1
    Now I know he's meant to be all older and in MGS4, but it's just got to the point where his voice is so gravelly it's annoying and hampers Hayter's ability to sound convincing.
  • EVERYTHING IS BLAMED ON MOTHERsmurfING NANOMACHINES. It's like a Deus Ex Machina, except it applies to the whole pissing game. It's total nonsense.
  • I complained about this after MGS3 came out, but what the hell happened to the whole 'tactical espionage action' part? It's turned into a goddamned third-person shooter. You're no longer encouraged to use any form of stealth at any time, and indeed the game gives you weapons and ammo at every oppurtunity. On the lower difficulties you can gun your way through pretty much every bad situation, whereas if that happened on the original, you had to hide or you were pretty much smurfed.
  • The plot. I don't think anything else needs to be said there.
  • Snake is a total pussy. Part of the character's appeal in MGS1 was the fact that he didn't give a toss about any of the other characters (including Meryl, until later on in the game), and would openly call Otacon an 'idiot'. By MGS4, he's some kind of altrustic second coming of christ with a massive hero complex who just takes from everyone and goes all emo and WHY DO I FIGHT ;_; I felt sorry for the guy.


And I can't think of anything else at the moment. Feel free to make a tldr point-by-point debunking of everything I said, in which case you probably need to re-think your life goals.