Did the Power Rangers ever do an underwater episode? If not, I guess this is how it would have looked. Swimsanity from Decoy is a shooter cum brawler that goes into the deep to find reference for its bad guys and monsters.
This early look is indeed pretty slick, I like the enemy representations and the ability to play four-player with benefits of working together. The character graphics are currently pretty feeble, but hopefully there's time to bump them up and improve the swimming animations.
All in all though, somewhere between Smash Bros and Aquaman, we appear to have a cool new arcade game on the horizon.