When I played MGS2 a couple of years ago I did not read anything about it. Just bought the game based on "Metal Gear = Solid Snake = I like Solid Snake" logic. IIRC, the back of the game box did not feature any Raiden screenshots, but I could be wrong. I was not exactly prepared for the sudden switch from Snake to Raiden. I'll admit that, at the time, I felt like someone just massively trolled me :D

edit: in my own defense, I did complete the game but I still have no idea what the ending was supposed to communicate...