Hammerfight is about 2D battles of flying machines equipped with various slashing, piercing and blunt weaponry.
Want to give a ten, but is a little too flawed for that. I love the gameplay and visuals here. Is just so satisfying to use the mouse to kill stuff.
Can be hard to calibrate, though, and is punishingly difficult at times. If you just want a good action game, though, there's few that offer as interesting a gameplay mechanic.