Probably you are familiar with Netduino hardware. It is an open source 32-bit MCU based platform which can be programmed using .NET Micro Framework. Its like Arduino but more powerful as it is ARM powered. So couple of friends (Fabien and Bertrand) have designed a game console along with software framework.
It allows fast step in in to game development. Programing language is C# which makes great resource for learning new stuff. Game expansion PCB for Netduino has 2 analog joystics, 8×8 LED matrix, speaker, SD card reader. It can be battery or wall adapter powered. Wouldn’t mind a better screen resolution instead 8×8, but still this should be fun playing with. This is an open source/hardware project which seems to be actively maintained.