Developer: Creative Patterns
Platforms: Windows, Xbox 360
I can't believe I haven't suggested this already.
QuadSmash is a frantic arcade game with a strong multiplayer orientation. Players control crazy-fast vehicles battling against each other in epic matchups. Your vehicle can ride upside down and emit shockwaves, it has an energy grapple and a powerful dash to smash the ground. The main game mode, and the most enjoyable, is called “Smashball”. It’s a ball game in which each team must score in the opponent's goal. There is also a Deathmatch mode (actually a “last one standing”) for more destruction-oriented games. QuadSmash also features a full single-player campaign.
Quadsmash is a physics platformer originally released on the Xbox 360 Indie Games Channel. I picked it up a year or two ago for 400 points ($5), and it's easily my most played Xbox indie game.
The game has great, high quality art and music, and the platforming gameplay in the single-player campaign is surprisingly deep. There are a couple of neat mechanics (like the grapple beam), but what makes them stand out is that they can be used in multiple ways, for different things.
The single-player game mode consists of 10 progressively challenging stages which should keep you occupied for a couple of hours; despite the length, in my opinion the game is totally worth the $5 you'll pay for it on XBOX just for the solo mode. However, that's not where this game really shines.
This is hands-down the best multiplayer you can get for under $10. I've only had the opportunity to play with one other person at a time, but we've sunk hours and hours into the three multiplayer game modes. I can't really describe how awesome it is in text; you'll just have to check out the demo and see for yourself. The multiplayer more than justifies the $8.22 price tag for the PC release, provided you have at least one other person to play it with.
If the video below doesn't play properly, you can also find it here