The libGDX project is a cross-platform game development library written in Java, with some JNI code for performance hungry sections. It abstracts away the differences between writting desktop, Android and HTML5 games based on standards like OpenGL ES/WebGL. Applications can be prototyped and developed entirely on the desktop, then only 6 lines of code are needed to run your app on Android or HTML5.
This engine is perfectly suited to my needs. Everything works very well, it is completely flexible, contains lots of support for third party libraries. Most importantly for me, it got rid of weeks of work implementing OpenGL, audio processing, allows for publishing on a wide range of platforms, all without the annoying, often incompatible, and very strict developer interfaces and heavy engine code (which often isn't even used) from engines like Unity. Couldn't think of a flaw to name so far.