The library thing is huge. If you're in C++ land you've got UE4 and a large number of open source graphics engines (Ogre3D), plus far more options in every category of engine (OpenAL, Box2D, and so on). If you're in .NET/Mono land you've got Unity and a plethora of engines built around Unity.

It's ridiculous how much work these engines will save you, once you know how to use them, but ecosystem is key because these engines are HUGE.