The Thumby Color is an excellent learning and hobbiest development device, having the computing power a just shy of a PlayStaion 2 running at extrememly low power. You can make very beginner friendly games and very advanced depending on your interests, and can modify the engine and make your on native accelerated modules.
I was able to render full 3D scenes and have some limited raytracing support, despite the incredibly small size. Would highly recommend from beginner to expert.