Missiles, for instance, don't work very well underwater. Plasma and laser, however, do. Two of the weapons available. You can also pick up a speed booster which allows you to fly faster. In fact, it is essential on the ocean level.
Barrage includes support for multiplayer.
You can play all the levels except Tunnel. There is also an extra level included solely for multiplayer which looks somewhat like the Niagara Falls. The main difference between multiplayer and single-player, aside from the obvious, is that you now have a limited supply of ammunition on all weapons except the laser. Weapons and powerups lie scattered throughout the levels and you collect them by flying through them. During setup, you can choose which weapons to allow in the game and if there is to be a kill limit.