Now this game, I only bought it for the original Incoming as many others did as well, so I will review the first game as i didn't bother to play much into Forces.
Short review: Just get it if you like fast paced Arcade Shooters with an okay story.
Long review: The game itself is a pretty straight forward Attack/Defense game where you can control various air and ground vehicles, and sometimes also can control several units in a strategy minigame in the story. While the Arcade mode is what the name says, just flying around with an airplane and collecting points. Imagine the game being 'Alien Invaders' with 3D graphics and more variation on vehicles to choose from. The story btw is nothing which will blow you away, just the generic 'Aliens invade Earth' story, but the way the gameplay works here, i recommend a gamepad, best experience, and your triggers won't work if you play with xbox pad, but other than that you don't need much buttons anyways.