Just Deep Blue for some reason. The approach-avoidance of this game is pretty awesome, and I really do like the fact that I don't have to run-and-gun fire 24/7 on this shooter. If you accept you are in a sub and treat it like one you are good. After you actually power up on levels 2 and 3 it really does become interesting.
I think the reason why people don't like it is because of the speed. Once you get the power-up it does make the game more fun, admittedly, But overall; this isn't your average shooter. It's a submarine after all...