This game was absolutely beautiful. The environments were all impressive, the graphics really pushed the limits of the 16 bits. You use your sonar as well as sudden bursts of speed to hit things with your nose to kill enemies. A lot of enemies you're simply better off avoiding than confronting.
In some ways you could dismiss this as yet another sidescroller, but the underwater environments give things a different feel, allowing you to move freely up and down as well as left and right. The controls are at times a little clunky, this could have benefited from an analogue controller rather than the directional pad the Sega controllers had. This game is kinda a ball buster at times, but there is something about the feel and the look of it that keeps you engaged, even when it gets hard as hell.
Other than the Sonic games, this is to me the number one game I think of when I think of the Genesis. If you've never played this game you should definitely give it a shot.