Before I start, I just want to say, this post is reflecting my own opinions about different game engine and it is not intended to be taken beyond that scope.
I had a chat with Dan (a friend of mine at the Game Innovation Lab) about how many new game developers don’t know a lot about different game engines. Once the discussion ended, he asked me to post about game engines, and rate them according to difficulty and complexity. Nowadays there are more game engines than in the early days of indiegame development. The funny thing is only a few of them are popular such as Unity, Unreal Engine, and Game Maker.