It really pains me to say this, but I agree with Yahtzee on just about everything.
I always called BS on Metal Gear being a '99% movie/1% game' series, but MGS4 is pretty much that. I didn't realize it until the very end of the game, but if you play through the whole thing while skipping each and every cutscene, each act will last you somewhere around twenty to thirty minutes, resulting in a game that will only take about 2-3 hours to complete.
I really wish I was kidding. I loved MGS1 and 3, and I'm playing through 2 right now and I'm very much enjoying it, but MGS4 is just completely unbalanced. You'll play the game for just a few minutes and then get cutscenes that last somewhere around fifteen minutes shoved down your throat. You'll be saving more often than not because once it's all over you just need to take a break from sitting down. I know! You actually have to take a break from a GAME! It honestly puts my balls into a twist.
Worst of all, the story. Normally, I love Metal Gear Solid stories, because it incorporates real world politics, character development, and interaction down to the nail. To me, it's just fun to see characters go from one standpoint to another in a very coherent fashion from beginning to end.
However, MGS4 is nothing but a celebration of the past games in the same vein as Umbrella Chronicles. You'll have more references to MGS1, 2, and 3 than you will actually have original plot details. Even then, the original plot is as uninspiring and dull as it can get. Characters barely develop, everything politically related in the game is entirely fictional instead of having actual facts with small fictional icing... it just goes against everything Metal Gear Solid was originally capable of doing.
And as I've said before, MGS4 does nothing for you in the gameplay department. Each gameplay segment is ungodly short, the controls are stiff as hell, and even though the team tried pathetically hard to make controls that rival TPS/FPS games of today, you rarely get to actually use them. Some segments peg you against enemies like the Geckos that are completely immune to just about everything you have as well as enemies that that travel in tight-knit groups, so killing one sets off everyone else. You'll just find yourself ducking in a corner waiting until you can just walk by everyone.
Lastly, the design results in 0 immersion. At one point, you're in the middle east. Then bam, you're in South America. Oh wait, now you're in Europe. Hold on, Alaska! Now we're in the ocean! The settings change with each passing minute, making you feel that instead of one definite plotline you're trying to conclude, you're just killing time. A new scenario is dropped on your head like an anvil on top of the Wile E. Coyote, allowing no immersion like the past Metal Gear games whatsoever.
I really wanted some playtime from my PS3... but it looks like MGS4 isn't that anymore. So far, I'm enjoying MGS2 more than 4, and I'm only about two hours into it.