I'm very much a beginner with C2. I think it's really easy to make a 2D game with C2, but they are very bland in their presentation. I have found a few videos here and there that show some ways to make the game "pop" more, but they all seem like one-trick ponies. I'm hoping a major focus with C3 is making it easier to make the game look great. For example, particles with lighting baked in (shadows, reflections, the whole thing), heck even just plain, straight forward lighting aside from particles would be great. I tried using a light source in one of my practice projects and all I got was a bunch of really weird black shapes covering a bunch of the playing area. It wasn't very intuitive about why I got those results.
Also, RGB assignments for sprites that can be set up as ranges with the ability to randomize. <----This single thing would go a long way in getting more mileage out of the precious assets that take so much time to create and perfect and then have a lot less objects cluttering up the project simply because they are a different color scheme. It would make things like biome generation so much easier. If nothing else, please consider this for C3.
I imagine there are methods I haven't yet discovered to do the things I just described. Regardless of what C3 eventually brings, I'm glad to have a shot at making a decent game just being a game designer and not a full fledged coding expert. Thanks, Scirra!