This game...I really don't know what to say. I'm a fanboy of MGS, so I'll let you know that right now, but if you're the same kind of fanboy like I am, then MGS 4 is obviously the game for you. Reasons? Well...let me explain.
WARNING: MASSIVE SPOILERS AHEAD!!!
1) Rex vs. Ray
Ok...don't lie, I know ever since you were shown Ray on the tanker in MGS 2 you wanted to see who would win in an epic fight of Metal Gears. Well...not only do you get to see who would win, but also get to control Ray for an escape through Shadow Moses (yes, you return to Shadow Moses!!!) and for the fight with Ray. The fight is nothing short of completely epic in the way that it's done, and it seriously has me begging Hideo to become a movie director.
2) Everything is explained...albeit if confusingly
Yes, everything is explained, from the Patriots to what has happened to Fox Die. One thing I really wish they would have included in this is the demo theater that they had in the special editions of the other two PS2 games, but I have a feeling that that will be included in the later version of this game. The reason I would like the demo theater (in which you can view all cinematics) is that sometimes (such as near the end) the plot gets so confusing and convoluted that I would like to be able to sit down and watch it again. The only thing I can recommend to people is that they create a new save game every time they save, so that way they can go back to play a part that they loved to play (such as the motorcycle chase scene, the Rex vs. Ray fight, the Liquid vs. Snake fight, the cinematic trot through the microwave hall...etc).