Originally flash games were 2D so they could run on any computer without much effort. However, modern technology allows optimizing 3D games to the level of their ancestors. With extra dimension, players will face more problems because they must control additional coordinate. If earlier you could only fall down from one position, now you can do it in two different ways. The 3D world has its positive sides, as well. Player has more options for maneuvers which add freshness to the gameplay. Racing, shooting, fighting games… They all seem more amusing when you try them in 3D.