It isn't just the first person perspective thing. The tranqualizer gun, the lockers, the rails, and the first-person aiming are now all part of the gameplay. They work better in MGS2 because the rest of the game was designed around them, but in MGS1 they reduce the stealth aspect of the game, not to mention the challenge, greatly. Because the AI of the guards was upped, while keeping the areas the same size, it's easier to dispose of guards than to sneak by them.
That doesn't necessarily make it a bad game, just a different experience from MGS1 on PS1 (and a slightly inferior one, IMO).