Since it seems pretty clear that HTML5 is the better technology to use going forward, does anyone know of any good development tools/environments for game development in HTML5? One of the things that was initially drawing me to Flash was the wealth of development tools available that make game programming intuitive (and Adobe's own Gaming SDK). Since HTML5 is still relatively new, there doesn't seem to be much in the way of development environments and the JavaScript language (in my opinion) is just not well suited to game programming or development of large applications in general. At the moment I am currently working with the basics such as a text editor, Chrome's debugger, and IIS. While it works, more sophisticated tools (for debugging especially) aimed towards application development would be nice.

If you are interested in using Phaser, you may also consider using HaxeFlixel, PhotonStorm was a long-time user of the Flash Flixel framework before he decided to port it to HTML5 as Phaser. Similarly, HaxeFlixel is an evolution of Flixel, supporting native Windows, Mac, Linux, iOS, Android, BlackBerry as well as Flash and HTML5

I have heard a lot about Haxe and it definitely sounds interesting. I remember hearing that the developer of Papers, Please reportedly wrote that game in Haxe. Is the language better suited to modular development than JavaScript?

Papers, Please was developed in Haxe.

I personally feel that it is good for modular code. There are many language features (some awesome for everyday, some are better for that "one time" you really need them) that makes it simpler for me to control how my code relates, and how it outputs. Haxe has a tool called "haxelib" which helps you install libraries of Haxe code, which makes it simple to share code with others, or plug in someone's library. With dead-code elimination, only the code you use is compiled your final JavaScript.

This is somewhat anecdotal, but this is a post someone made recently that made Hacker News. They were comparing the performance for a video decoder, using Dart, asm.js, Flash, native C++ and Haxe to JavaScript, it was pretty interesting: http://www.infognition.com/blog/2014/comparing_flash_haxe_dart_asmjs_and_cpp.html

The native debugging depends on the target platform. If you use the Flash target, the standard Flash debugger and Adobe Scout all work. When you go to JavaScript, there is something called "source mapping" which helps debugging match back to your original source. This is supported in Chrome and Firefox. It's the same tools you would use for regular HTML5 debugging.

HTML5 is highly advertised technology and very hyped, but essentially it is in evolving state right now. It is not mature or stable in any way. They promised all of the Flash capabilities but good luck to see decent HTML5 games made by hobbyists (Zombotron says hi). Technology is not mature at all. A lot of browsers have issues with basic HTML5 stuff, even with Canvas, which were introduced several years ago. The situation is especially sad on smartphones, where you can only play very basic games in browser (think three in a row genre without fancy effects, poker with dozen bitmaps and so on). Anything more complex than that will kill the battery and will be rendered like a slideshow. Someone mentioned low-end devices here? Yeah, sure...

However, if we are talking about Flash technology, it is still much more performant and stable than HTML5. Asm.js may change this, but I don't see this technology being active on smartphones for 1-2 years. Not to mention that you can wrap all of your Flash games into AIR applications, which can be freely run on any mobile device with ARMv7+ if I recall right. And you can do it right now with almost no restriction on fancy effects and mechanics. Especially considering the fact that AIR applications can utilize the power of mobile GPU, which is more performant and battery-friendly.