THE GOOD:Beautiful graphics. Tight, responsive controls and gameplay that has been refined from every game in the series. A real feeling of progression and evolution in the franchise. Grade A voice acting. Epic cinematics, and epic conclusions to each act.
THE BAD:
Cutscenes are LONG and if you are not a die-hard fan this might turn you off. You can go for an hour and a half (straight) without playing if you watch all the cutscenes. The over-the-top and confusing plot is not friendly to newcomers to the series, and even some die-hards will have trouble making sense of it. The boss characters are not as memorable or as fun as previous bosses. HIDEO KOJIMA CANNOT WRITE LOVE STORIES!
SUMMARY:
MGS4 is the conclusion to Solid Snake's story. It is his final mission, and it is suitably epic. I won't go in to spoilers here, but suffice it to say, every act in MGS4 could stand alone as its own game. Every act has an ending that entire games wish they could have. The game just keeps getting bigger and bigger and more epic and it's almost too much to digest.
Nearly every character from the past games is given a little time to shine. All the loose ends are wrapped up in one huge, explosive adrenaline rush of a game. Let's just say that after playing this, if you didn't like Raiden in MGS2, you will LOVE him in MGS4. Also, you will see many characters who you wouldn't expect. The story is everything but predictable.
The gameplay is vastly improved over MGS3. Camo returns in the form of OctoCamo, basically automatic camo that changes depending where you are. It really speeds things up, not having to go in to the pause menu to switch camos all the time. The backpack-style item management is back, though. I personally prefer MGS1 and 2 style, but I can see how some people would get annoyed having to scroll through so many items.
The camera can now be controlled with the analog stick, allowing you to get a much better view of the battlefield. This makes sneaking infinitely easier, so you don't have those frustrating moments of running right in to a guard's line of sight simply because you couldn't see him due to the angle.
A new mechanic, the 'threat ring', has been added. When lying down or crouching, a white ring will appear around Snake. Peaks will appear in the ring in the direction of a nearby enemy. It can be useful if you don't want to use up battery power on the radar, but battery power recharges so quickly that I still relied on the radar more than the threat ring throughout my playthroughs.
The radar is more in an MGS3 style. I miss the soliton radar of MGS1 and 2, but that would probably make this game too easy. The soliton radar allowed you to see the enemy position and their field of view on a clean map of the area, while MGS3's assorted radar/sonar equipment just showed the relative positions of the enemies, with no map. In MGS4, the Solid Eye's radar shows the relative positions of nearby enemies, as well as bursts that represent loud noises. The radar also indicates how much noise you're making, so if you see the noise ring around you begin to grow, you know to slow down or crawl so nobody hears you.
Noise and smell come in to play when it comes to enemies detecting you, which I thought was a very interesting mechanic. It makes the game a little more difficult, but a lot more rewarding when you manage to sneak away.
The shooting mechanics have vastly improved, finally allowing you to move around while shooting in first person mode. Also, the ability to shoot while rolled on to your back on the ground is a saving grace when it comes to avoiding alerts.
Essentially, every aspect of MGS4's gameplay feels extremely fine-tuned, tightened and refined. It is very much the MGS formula, but honed to a keen edge, sharpened to perfection. The only downside is it's so good and so responsive that it makes the first 3 games hard to go back to.
I highly recommend re-playing the first 3 games in the series before playing MGS4. Not only will you be able to understand what's going on, but nothing, NOTHING can beat the 10 years of nostalgia channeled in to Act IV of the game. I don't want to spoil it for you, but... wow. If you're a fan of MGS1, Act IV will blow you away.
Really, though, this can't be said enough: DO NOT PLAY MGS4 IF YOU HAVE NOT PLAYED THE FIRST 3 GAMES IN THE SERIES! About 80% of MGS4's story relies on the fact that you know what happens in the first 3 games. Pick up the MGS Collection and burn through it before you try to tackle the behemoth that is MGS4. Reading summaries just isn't enough to give you the knowledge you need going in to MGS4.
If you're a fan of MGS at all, MGS4 will blow you away. It is fanservice in a lot of parts, but it is glorious fanservice that treats the characters well and offers a fitting, epic conclusion to the arc of the legendary Solid Snake. A must-have for any PS3 owner.
Also, a huge bonus is the fact that Metal Gear Online is included free with MGS4. This game is an excellent multiplayer tactical shooter, in the same vein as the MGO that was included with MGS3: Subsistance. However, MGO's controls are vastly improved (as they are the same as MGS4's).