A few months ago I built my first HTML5 game, to see how capable the browser is these days. Then I decided I'd like to target more platforms and discovered Haxe. I've been pleasantly surprised by the language and tools, and thought I'd share my experiences porting the game. If you have any questions, let me know!
You should definitely give it a try. If you have any experience with the Flash API, NME will just work like you expect. I didn't, but found it easy to learn with Adobe's online documentation. There's several higher-level game frameworks available as well, and ports of stuff like Box2D for physics, etc. I think it's shaping up to be a pretty compelling platform.