It's not a bad game, but there can be some improvements made. I haven't read everybody else's post, but I'll give my opinion on it.
Don't expect something like Call of Duty 4 or Resistance: Fall of Man multiplayer from this, you'll be disappointed. It's a much slower type of game, I guess you could say it's a little more tactical because of that and because of the SOP (Sons of The Patriots) gameplay mechanic, which has you pressing triangle when grouped with team mates to 'link' up with them and you can see them through the map and there will be alerts if they're in trouble and stuff like that.
Graphically, it looks good. The maps and characters have lots of detail, but there really aren't many graphical effects so it feels a little lacking in the "ooohhhhh's" and "ahhhhhh's" department. The sound effects aren't bad, but I for one would be overjoyed if they added more death screams because it's like you only hear the same screams over and over again and that gets annoying when a bunch of people get hit within a short time.
The controls are complicated, but it gets better as you get used to them. Not only that, I would imagine that getting used to the controls now will put you a step above non-beta players when it finally comes time to play through MGS4. The biggest problem I have with the controls would have to be how the auto-aim feature works. What happens is that when you select auto-aim and then press L1 to bring up your gun, the camera will be move and lock behind your character. This is a big problem for me because I use my camera to keep an eye out on my environments and if I see an enemy, I'll react by pressing L1, but it usually screws me because now my camera gets locked behind the character instead of the character turning to face the camera direction. The way to get by this is to not be eager to press L1 and instead, face an enemy first before you try to lock onto them with auto-aim.
Talking about auto-aim brings me to the next point, the actual combat. I haven't used all of the CQC and weapons yet, but my biggest complaint is the shooting. Auto-aim seems to be very difficult to lock onto somebody and feels rather finicky about when it wants to lock on. This is bad because I find that unless I get a headshot, auto-aim is the most effective way to actually kill somebody. Aiming over the shoulder or in first person doesn't feel effective at all and unless you happen to get a headshot. It feels like unloading your entire magazine into the enemy wont do much of anything. Lastly, I think that they should do something about the health because I don't believe there is any way to get more once you've been hit. I wouldn't mind regenerating health, but I would at least settle for health packs (unless you can actually get more health and I have no idea how).
*edit* Oh man, I have to make an edit here to briefely talk about grenades. I haven't used them all yet, but they feel so ineffective against enemies. I can throw one right at the feet of one or more enemies, it'll blow up and send them flying (sometimes humurously smacking them into walls) and they get right back up.
Lastly, does anybody know what you have to do when you're being choked in CQC and the image of the left analog stick comes up on the screen? It looks like you have to shake it left and right, but I do that and it doesn't look like anything happens. I think that I would rather just let myself die because I'm using my brand new Dualshock 3 after the left analog stick on my Sixaxis is now off center from being too hard on it, I don't need to bust my new controller too.