Ecco is a very original and hellishly hard game. You control Ecco the Dolphin, navigating the waters, saving other trapped dolphins (which of course were left on their own here), finding key diamonds, schools of fish and pockets of air deep down in submarine caves.
The movie might look a little clumsy with the player hitting walls all the time, but there's no other way: Ecco has tremendous maximum speed, but no brakes whatsoever. The fastest way to slow down is simply running into something.