Hybrid Heaven doesn't have terrific graphics (which Dale described as 'bland') and it doesn't have a great control scheme either. But it does have an excellent storyline (unfolded through some of the best cut-scenes to grace the N64), emotionally complex characters and some interesting ideas towards gameplay.
The developers, KCEO, obviously set their sights high for this game. One look at the cinematic intro for the game and this point becomes apparent. Its length and use of voice-acting is initially very impressive for a cart-based game, but upon further inspection, it becomes a metaphor for the rest of the game and is ultimately what's wrong with Hybrid Heaven.
According to ESRB, this game contains: Animated Blood, Animated Violence, Suggestive Themes