What are some alternatives?
When comparing PlayN and Unreal Engine, you can also consider the following products
Unity - The multiplatform game creation tools for everyone.
Pygame - Pygame is a set of Python modules designed for writing games.
Blender - Blender is the open source, cross platform suite of tools for 3D creation.
Castle Game Engine - An open-source 3D/2D game engine for ObjectPascal.
GDevelop - GDevelop is an open-source game making software designed to be used by everyone.
CryENGINE - The most powerful game development platform is now available to everyone. Full engine source code.