Seaman
If you only play one game on the now defunct Sega Dreamcast, I cannot recommend Seaman enough. It is unlike any other experience. You plug a microphone into your controller, and raise the titular creature from birth to death, speaking with him about, well, everything along the way. He completely, magically understands you — I told him my favorite movie was The Matrix and he referenced the film! In a just world, this game would be in a museum.