about 2 years ago I bought a CryEngine book very cheap (< 3 USD), and tried the SDK (it was free at that time), but was unable to set up the asset pipeline, even after I installed some software without very clean licensing background (of course I removed them afterwards). from the programming side Lua seems to be a bit annoying interim step, the book mentioned it as much slower than C++, so better to minimize its usage, just link the C++ stuff via Lua. probably fine and fast for prototyping.

personally I liked the editor, but did nothing deep. and the lack of documentation and tutorials kept me to stay with 3dgs, and then started with UE4 immediately when it was released, whose programming was also difficult for me in the beginning (and was undocumented). it requires a lot of reading and planning before moving on, but recently I have started to enjoy it as I remember Unity3 was much easier to start with, but the Pro price of 3-4 was too high, and 5 came too late after UE4 to try.