Guys, honestly it is no matter which one game engine devs choose. It is the only platform to develop games, collection of features that you can use and you don't have to implement it by yourself. You can develop everything by yourself with no huge/complicated game engine, even with no game engine at all. It is only a matter of time needed to develop game functions. Game engines are frameworks, it provides you some functions like implementation of collision detection algorithms, so you don't have to do it by yourself. It makes developing faster and easier. It have no impact on the visual aspect of game - it is a job for the rendering engine and like with game engine, it is the only collection of implemented algorithms that will calculate how visual and graphic effects will be rendered. For physical effects calculation you use something called physic engine - it will calculate moves of interacted objects and so on before data will be processed through render engine. Some game engines provides integrated rendering engines some don't, that's why you can see some support only 3D content, some 2D or both. If devs chooses Unity it is more about that it have features, that they think, will be best to cover game mechanisms with reasonable amount of work needed from the devs side.
