Actually, I did look into cocos because RoboVM is still not cosidered proven and I plan to develop or port to iOS at some point.
The main problem is googlability (did I just invent a word there?) of cocos stuff. Google is indexing all the old cocos iOS stuff higher and it's really hard to find anything, especially if you never did develop for iPhone and have no clue if the article you're reading is about old or new cocos. The docs are great, but often you need to find examples of different specific topics and those are usually on someone's blog or similar page where only Google can take you. Also, on some forums I found this way, people were trying to help cocos2d-x devs, but those helping were iOS devs and answers were like "this is the way it works on iOS but YMMV", as they were unsure if the API has changed or not.
Maybe it's a great library, but all this left me with too much confusion, and I picked something that was rather straightforward and still supports desktop and iOS if I decide to port.
I've had similar problems googling for Cocos2d help. OTOH, because you can run the CocosBuilder-generated game in the browser, it is very easy to experiment in the JavaScript console and figure out how the various JavaScript bindings of the C++ classes work.
My own judgment is that it's relatively difficult to get a Cocos2d project to work across all platforms (HTML5, iOS, Android). But once it works, the development iteration loop is very comfortable and fast, because you just refresh the browser to try the current version of the game.
CocosBuilder is now abandoned, I think. The creator is building something similar (cocos2d only, not cocos2d-x) and the cocos2d-x guys are building CocoStudio (Windows only, no javascript, for now). Although I love the idea working with javascript for cross-platform development, the whole project feels immature.
