Warhawk is a multiplayer only game and is a great deal of fun.While battalion wars 2 has a single player and a mulitplayer.
BWII will have online while Warhawk is only online.Warhawk's gameplayer is sort of based more on skill, while BWII has a rock paper scissors format (i.e. anti air always beats airborne helicopters and tanks always beats infantry).
I will be buying both.I didn't purchase the first battalion wars manily due to the abscence of multiplayer but, I loved advance wars DS.Warhawk is a fantastic multiplayer only game it does take a while to get used to the controls.I don't use the motion sensing in the sixaxsis because it is very difficult to mange shooting and keepin the warhawk steady.
I do have some complaints like yesterday I blew up a warhawk with a sniper rifle! Also in small deathmatches you respawn right next to your enemy.So you can imagine what that can be like.Other than those small complaints this is a great game and I highly recommend cheking it out:)