In the near new version for unity, 4.3, we can use new tools for 2D games like sprites tools. This will do the 2D development really easy (so that 3D unity games). In fact I had doubted about use unity by the problems with the 2D characters creation (this is really easy in new unity 4.3 version) and I had yesterday working in concept game in game maker, a good game engine, but this offers any limitations to develop any of my ideas.
I am really happy with this new unity release and I´ll wait to begin with the game develop to the unity 4.3 launching. By the way I am doing the pixel art and 3D design of the scenes. To work! :)