Technically and structurally fundamental for visual novels and puzzle games to come, but insanely difficult to complete without a guide and with a main character whose fundamental traits revolve around dealing with serious moments by acting like a lecher. Not even kidding, almost half of the game script is about sex jokes, and not even funny ones.
The pixel art, music and general ideas are stunning, but ultimately misused and relevant only as the solid foundation they represented for eroge to come.