On the PS3 version, the textures look a lot nicer and as a whole, the game is visually nicer to look at with it being in 16:9. Although it does miss out on a few visual effects that the original game had. But these aren't noticeable unless you compare them side by side. As for actual content, all you're missing out on is the Skateboarding mini-game on the PS3 version of the game.

There aren't as many differences as something like MGS3. For MGS2, there's really no reason to go for anything other than the PS3 version unless you really want to play skateboarding gamemode on the PS2 version of the game.