I would probably say the REmake or RE4 GC.
The REmake along with Rougue Sqaudron II, were the games to convince me how powerful the GC was in comparison to the Dreamcast (graphically I wasn't that impressed by most early PS2 games).
RE 4 GC showed me what could be done with then current gen technology. I honestly didn't think a Resident Evil game could look that good in real time (when I first saw shots of RE4, I thought quite a lot would be pre-rendered). Then Capcom ballsed up by not having proper widescreen until the Wii port.
However, I wasn't gaming when the original was released on the PSX, so I can't really say what impact it had on me. But it must have been fairly revolutionary as if I remember correctly didn't it convice SquareSoft to use pre-rendering for FFVII (and therefore influence it jumping ship to the Playstation)?
