This is an interesting thread. I've been using C2 for a little over a month. I love it. I tried unity, gamemaker, etc.. C2 was the most intuitive and quickest to pick up. I tried CC as well (cause I wanted shaders and lighting) but found it tougher. Mainly because I tried C2 first. ;)
As far as HTML5, WebGL, etc. I'm 34. I remember when people thought flash, AS & java were weak. Within a short time they became quite powerful. (and supported) I'm a graphic / web designer by trade. (primarily mobile) I can Honestly say that sticking with HTML5 is a wise choice. It's getting better everyday and has obviously made an impact to where it threatens Flash. (well actually Apple threatens Flash) WebGL is going to get better I can promise that. The mobile market (as sad as it is) dictates a ton of our technology. Including the gaming counsels, and PC. Steam has a counsel coming out, there's OUYA too. The support for the features CC seems to have over C2 and WebGL is only going to get WAY better. The market is asking for it. It take a little time but I bet the farm that within 6 months.. we'll be seeing everything we want in C2 come to life. Granted there are some limitations atm but it will get better.
If you are considering writing your own game engine. Here is something to consider:
He makes a great point. program with whatever, use what ever can get something on the screen the fastest and make a game. It's really a matter of what you are comfortable with.
I'm excited every day to come to Scirra's site and see what's new, what people are working on, and the problems and solutions that come out of it. It's innovation and growth. :)