Activision was always known for creating creative games with unique gameplay concepts, and Dolphin is no exception. Dolphin may very well be the first (and only) game to incorporate sound as part of the gameplay. For you see, Dolphin much more than your run of the mill action game.
The concept of Dolphin is simple, guide your dolphin through the holes in the seaweed walls and out swim the squid. The problem is since your traveling at breakneck speeds (does a dolphin even have a neck?), you need to know where the hole in the wall is before you see it! This is where the whole sound concept comes in. As your zooming along you'll hear a tone, the pitch of this tone indicates where the hole in the wall will be (the higher the tone the higher the hole). This is supposed to simulate the dolphin's sonar, but what it really does is make you think before you react. If your dolphin misses the hole in the wall, he'll slow down a bit and the squid will move closer.
However you can speed yourself up (and slow the squid down) by catching ocean currents. These ocean currents are represented by arrows the float across the screen. An arrow pointing to the right will speed you up, while and arrow pointing to the left will slow you down. However since the squid mimics your movements, you can trick him into being hit by one of the slow currents and send him back a few inches. If the squid catches your dolphin it's game over (who knew squids ate dolphins?)!
Thankfully you are not alone in your quest, every now and then your friend the seagull will fly across the top of the screen. By jumping out of the water and touching the seagull you'll gain the power to destroy the squid (think of the seagull as a power pellet for your dolphin), but be careful that your power doesn't run out as you touch the squid. Another interesting technique for outsmarting the squid is to wait until he hits a good wave and suddenly reverse directions. This will send the squid flying to the other side of the screen while you're safely on the other. It's tiny tricks like these that make Dolphin a great strategy game.
One thing that programmer Matt Hubbard didn't realize is that if timed right, the player can actually jump over the seaweed walls! After getting the pattern down, the player can basically play forever (far out running the squid). Matt Hubbard has said that he would have taken this cheat out if he had caught it in time. I wonder how many people used this technique to get one of those coveted "Secret Society of the Dolphins" patches?