Pretend it isn't called Battleship or based on the game.
We haven't had a good Naval War movie in forever. And even then, it was a Submarine movie! Just enjoy the cool action flick with aliens in it.
Okay, let's assume that this isn't based on the game. We still have to deal with the fact that its THE NAVY FIGHTING ALIENS!!! Oh yeah, we've never seen a movie where our military had to stop an extraterrestial threat ... y'know aside from War of the Worlds, Super 8, Battle: Los Angeles, Mars Attacks!, Independence Day, The Blob, the list goes on! The only thing different here is that it's the navy, not the army. Sorry, but that's not good enough for me.
Besides, if there isn't any good naval movies anymore, why not go back to basis? There have been good naval movies to draw influence from: Hunt for Red October, Das Boot, The Battle of the River Plate, all good examples. They don't need to have aliens. In fact, they SHOULDN'T HAVE FREAKING ALIENS!!!