MGS4 would have been fine if the entire game was like the first two missions: A mercenary playground where your choices mattered, you could open fire on side A that belong to nation X, but then a mission takes place in nation X and they still remember what you've done. Things like that, just being part of an active battlefield, it would have really fit in with "War has changed" theme the game was setting up at the start.
As is, after the second mission the game just kind of shits itself and it becomes part nostalgia wanking trying to shoehorn in everything from the first three MGS games into this one, and then the other part is just tech test levels that felt like they were vertical slices to test some ideas or PS3's capabilities more than anything else. I didn't like a bit of it, I never had a PS3 so I never played it but lord knows I watched enough of the game. Multiplayer looked nice, but then again I said the same thing about MGS3.
Oh, and the devs are cowards for not letting Snake blow his brains out at the end or go with the ending where he and Otacon go to prison as terrorists. Would have been a fitting ending, a man out of time with no purpose left having everything catch up to him. Big Boss and Zero reveal were fucking retarded, I would have been pissed if that was the grand ending I would have seen in 2008. MGS2 or MGR are much better endings to the franchise as a whole and I wish they would have done more with Raiden