A good combination of elements from the first MGS and new ones, plus a much more in-depth plot...
Other than that, I really do enjoy this game. It has a little bit more linear storyline than MGS1, and it doesn't make you do anywhere near as much backtracking as the previous Metal Gear games have made you do, which I really think was nice... that stuff got a little old. This one had a fresh level almost the whole way through the game. Now, that may negatively affect replay value for some, but I don't mind it.
It was also a little odd that the majority of the game you actually play as "Raiden", not Snake. He is a younger character and whines a lot, unlike the much more gruff Snake... That all gets explained a little bit at the end, but still...
Son of a gun though... I really wish the ending made more sense.