just finished the game ( total game time was about 21 hours, including cutscenes and gameplay) and here's my review based on the single-player mode:
Graphics - 9.5/10
This game has some of the best facial and clothing textures I've ever seen - amazing! The lighting effects are breathtaking as well and really add to the atmosphere of the game while playing. The environments are very detailed and well modeled and again, the effects are simply amazing. Everyone with a PS3 should at least borrow or rent this game just to check out the graphics, even if you're not a fan of this type of games. The only few flaws were the slower frame rates during heavy on-screen action and some aliasing issues on certain objects, but everything else was done almost perfectly. Simply awesome.
Gameplay - 10/10
I love how you can choose your own way of getting through the game; you can either do the Rambo thing and kill everything you see, or you can play it like it's meant to be played - stealth all the way. This guarantees at least TWO play throughs using 2 very different styles. Perfect.
Control - 8.5/10
Having played quite a few 3rd-person shooters/action games, I have to say that while good, the control in this game COULD be improved. It's not always the most responsive and for a stealth game, doesn't have the most elaborate collection of stealthy moves. Compared to another PS3 exclusive, UNCHARTED, this game felt slightly sluggish and more restricted. Overall though the game controls very well and the gun fights, whether you're using the 1st person view or the 3rd person view, are very exciting to go through.
Story - 8/10
I've played MGS1 and MGS2, but skipped MGS3, and have downloaded the MGS database thingy off of PSN so that I could catch up on the story line, but still at the end of MGS4 I felt a little confused at some of the plots and twists in the game, and didn't quite understand all the information that was presented by the cutscenes. I think the problem with MGS stories is that they're too dense and you don't really have enough time to digest everything before more info is being thrown at you, and sometimes you have to accept some really far-fetched ideas so that the story can make some sense.
Overall though, the story is interesting enough to hook you in, and ties up all the loose ends from the previous MGS games. I wouldn't call it a brilliant story though.... but some of the ideas are interesting and should make a pretty good movie.
Sound and Music - 10/10
OH MY GOD. If you have a 5.1 surround setup you will absolutely love this game (Dolby TrueHD). The environmental sound effects, the guns, and the explosions are some of the best I've heard. Definite ear-candy if you have the right setup. Music, once again, is top-notch, and really gives the game a movie-like experience. This game and UNCHARTED are 2 PS3 games that should be bought based on SOUND alone - definitely worth it!
Cutscene and Voice acting - 8.5/10
Everyone should know by now that this game is almost half cutscenes and half gameplay, so it makes sense to have a rating just for the former. Overall the cutscenes are VERY well done and some are almost movie-like, and are worth watching through with great attention. Some though, are WAY too long and could use some editing for sure, so that the pacing of the game could be a little better. Voice acting is top notch, except for maybe a few moments where I thought it was over the top / too cheesy.
Be prepared to sit for a long time between gameplay, though. Some cutscenes are REALLY, REALLY long. lol
Overall - 9.5/10
The best PS3 game so far. Get it.