I highly recommend Silent Hill 2 if that's the case. Primarily because all subsequent releases of that game graphically altered it and removed a lot of the fog which was a huge contributor to the atmospheric feel of the game, but was largely implemented as a technical workaround so the poor PS2 wouldn't have to render everything and catch fire.

Very good game, but the genuine experience can only be had on the PS2. So if you're going to invest in that old hardware, make sure that game is on your list of games to pick up for it.