You can't per say go wrong with mainstream engines like UE4 or Unity or Lumberyard or (...). Choice of engine depends on many factors, what kind of game, what middleware you want to use, target platforms, how much you want to use various asset stores etc. Unity is great for indies, it's great for C# developers used to Visual Studio IDE, it's great for multiplatform development, you can achieve comparable results as with any other engine as long as you have muscle to pull it off, but how much of it is relevant for Em-8ER? Not that much. Similar can be said about other engines. I'm Unity guy, but completely understand Grummz's decision to go with UE4 for Em-8ER.