When I started work on Crowman & Wolfboy there had already been some development complete on the game. A few levels were already built and saving and loading were being coded. However we soon ran into several problems with development.
Documentation seemed really out-of-date with the original engine. Code wasn’t working as the documentation specified it should. Even the examples given didn’t work. It was a serious problem which made progress slow.
Not long after joining we started looking into alternatives. First, we came up with a list of requirements which an alternate need to meet to even be considered. With nearly all the art complete, the new engine needed to support 2D art assets. Nearly all engines are capable of this. A strictly 2D engine is the obvious answer, but 3D engines can be clamped into 2D so we didn’t want to rule them out. We wanted to target both iPhone and Android mobile platforms so solutions specific to one platform were quickly excluded. For example, when we were doing this Cocos2D only supported iOS and would require another separate engine for development on Android. Next, documentation needed to be current. This was the original problem we were trying to get away from.
From this list of requirements we narrowed the possibilities and eventually chose Unity. It is a 3D engine but has several frameworks for building 2D games. It supports exporting to both iOS and Android platforms. And lastly, documentation is excellent. As an added bonus, there is an active community using Unity.
Since switching we haven’t looked back.