C2 is the best 2D game development IDE, hands down. But, at the end of the day HTML5 is HTML5 - bugs appear in some browsers that do not appear in others, browser audio is terrible (causing many posters to complain to Ashley about C2 audio support not realizing it's the browsers themselves), graphics drivers seem to cause all sorts of weird issues with WebGL, HTML5 works brilliantly on deskptop but grinds mobiles phones to dust if you want anything involving physics or complex effects (vs native apps). The canvas tag still has weird limitations like no z-indexing...
HTML5 is painful, but it's going to get better I'm 100% sure. With all the browsers fighting over standards it's a bit of a wild west right now. I myself keep flip-flopping from throwing my hands in the air and screaming "I'm done with HTML5!", then realizing what a pain getting 2D to work in something like Unity is and then a few days later coming back to C2.