Heh. Well personally I think it's brilliant. You can manage your own base, build your own Metal Gear, over 100 optional missions that you will want to do. The co-op is really fun too and it doesn't just add the amount of players; it increases difficulty every time there is a new player. It plays like MGS 4 too.
The criticism I would give it, which I really shouldn't because it's a PSP port, is that some missions are really short (sometimes just one area) and Big Boss' face for the in-game cut-scenes is just the one static image. However I really do enjoy the animated ones which are 90% of the cut-scenes anyway.
The plot twists. Oh the plot twists!