Furious Angels [Steam store page]
Simple yet elegant gameplay. This is a great example of how to make a game engaging but super accessible.

The Binding of Isaac [Steam store page]
Decent mechanics but disgusting theme. Enemies can shoot diagonally, you can't. The bad hit-boxes on arrows are frustrating, making yours regularly miss enemies and allowing enemies to occasionally hit you through walls. Made with Flash, low res.

Beat Hazard [Steam store page]
An interesting mix of music and gaming - enemies generated by songs. Disappointing that they charge extra for multiplayer (DLC - BH Ultra).