Sound issues are a MAJOR problem, despite what folks like Ravayne claim, especially on the devices where HTML5 was hyped up as the end-all-be-all by Steve Jobs (iPhone, etc.) In other words, the company who championed HTML5, spreading a bunch of provable lies (about Flash) in the meantime, is THE WORST when it comes to HTML5 compatibility (a good chunk of the "standard" simply doesn't work). And even on browsers where audio is somewhat well supported, you often need to specify two or three different audio file types -- one browser supports MP3, another one OGG, another... you get the idea, and it's Apple who has the least support for the fewest types of files, and that support is itself a very limited subset of the HTML5 audio "standard".
People keep claiming that up-coming HTML5 standard X or standard Y are great reasons to ignore the broken promises of the past. In other words, it never worked to begin with and the "standards" have only gotten worse since, so for sure it'll be better this time!
Apple, via blatant thief (he said it, not me!) Steve Jobs, was responsible for delivering the initial pack of misinformation, but browser manufacturers have certainly helped to expand on them.
As a quick example, have a look at this site: http://html5test.com/
Another example for audio (in)compatibility: http://areweplayingyet.org/
And anyone who wants to dig up W3C documentation as evidence of a standard only prove their own lack of knowledge on the subject -- a standard on paper alone is no standard at all. Up-coming "standards" like WebRTC are just more examples what I'm describing.
Flash is your best bet for cross-platform delivery, power, and ease of production (it's an excellent platform for game development, and it's guaranteed to run on all browsers and on mobile as apps using the same code base -- little to no rewriting required). If you try something as simple as a spritesheet animation in HTML5 -- absolutely core to game programming -- you'll discover what a bad bad joke is being foisted on companies and game developers. This is why both Amazon and LinkedIn dumped HTML5 like a steaming pile of donkey turds -- the promise didn't meet reality.
If Flash isn't your thing, something like Unity3D is a great option that will work across browsers/devices and gives you plenty of space to expand when you want your games to have a bit more kick. I haven't worked much with it but I know for a fact that you'll have a much better time of it than HTML5.
Flash is available as a 100% open source solution (you can use FlashDevelop or Adobe/Apache Flex). I bet you'll find lots of commentary claiming the exact opposite, usually alongside claims that HTML5 is the best and only alternative. Lies lies lies lies lies...
Edited by Patrick B, 21 January 2014 - 03:04 AM.