I would be interested in your impressions.
After a day, I can say my first impression is me thanking myself for knowing Unity. I see nothing about C3 that would make me pay the subscription yet. I would never use this browser engine to create a large project. If I want to make asteroids or a match 3 game, sure, but nothing complex.
The UI is about the same as C2, but somewhere the designer forgot how to design. I won't mention those things here as there is another thread about it. The inability to test all features at the moment is hindering even if I understand their reasoning. I think they should have had an alpha test first with a closed group and then open it up to the public for beta-testing everything. Though not all things work, everything I tried seemed to be okay.
Importing sprite animations was fine, and using the behaviors was easy, but the pop-up window should have a list of behaviors to choose from or at least a plus button so people would know to click it. Right now it's just a blank window. If I had never used C3 before and clicked the Behaviors link and saw that empty pop-up box, I'd be like "um, where are all the behaviors?" (Seems Ashley is fixing this for the next build.)
I could go on, but no. C3 is not for me. I look at it right now as an engine to make browser games, not something for serious game development. But then again, I always knew that.