A great game, but not worth it without XBL.
The single player campaign, while fairly easy up until about half way through it, lacks substance. You go on a campaign of usually about 6 missions using a Hound of that role type, and the missions get harder as you go along. Completing missions earns you parts that can be used to customize your Hound, both in single and multiplayer.
While the single player is bare-bones, the multiplayer is a different story. You can customize your Hound from the Chassis up, adding guns and tools such as radar jammers or thermal cameras. Even the ammo is customizable, ranging from short range explosive ammo to ammo packed with Napalm.
Overall, I think Chromehounds is a decent game, and it's worth the $13 you can buy it used for from your local Gamestop. With some nice graphics and decent multiplayer, it's a good game, but if you don't have XBL, don't even think about picking this game up.