The parts that aren't open source are the google-specific pieces. Amazon has a thriving ecosystem (of mostly addictive micro-transaction-ridden trash) on top of their FireOS, which is mostly Android with the Google parts replaced with Amazon parts.
Still, Blackberry managed to make it easy to repackage Android (2.x) software to run on their QNX-based OS and there have been multiple demonstrations of Android software running on Linux with a relatively thin API layer. There's at least one commercial, IIRC, tool that does that for Windows.
Any system with a low barrier to entry will be flooded by games that are cheap to develop and quickly recover the investment. There are good games, but the platform is generally much less capable than either a desktop PC with a beefy GPU or a console.
