In short, for simple games:Is Flash still a good option for browser-based PC clients? It still has 90%+ penetration.What is a good alternative for mobile devices? Is HTML5 + JavaScript the choice for mobile? Or does one have to learn a new native language for each target platform? (Android, Apple, Windows Phone)...If you desire further background: There are more blogs about the official demise of mobile Flash than I can count, along with endless useless and vitriolic comments. I'm actually trying to do something practical: build simple games that can be served accross multiple platforms. Several months ago I plopped down $1100 for CS5.5 Web and am wading into Flash. Bummer. My question to people who actually develop simple games and apps: What platform should I use instead? Is Flash still a sensible platform for web-served PC users? For example, let's say I build a simple arcade game that I would like to serve as an app to mobile users and as a browser-based game to PC users. Should I still invest the time and effort to learn and develop in Flash for the PC users, while building a parallel code set in some other language for mobile users? My games are simple enough that it would be annoying but not inconceivable to maintain parallel code sets. 
What to use for simple cross-platform games instead of Flash?
mobile;flash
HTML5 and Javascript all the way! There are several 'game engines' using JS that you can download and play with. (Crafty, Impact, Melon JS, Akihabara) to name a few. Melon JS supports the 'Tiled tmx format for platformers and top downs. There is ongoing debate as to the 'web' technologies or native code question for mobile game / app dev and I think the concensus (and rule of thumb) is that if you need the hardware features of the physical device look towards naitive code. But if you don't need access to the hardware specific parts of the device, why not use a portible and web based solution? You will get more platforms with less effort. As for Flash (and Silverlight) going the way of the Dodo bird, its not going be be an overnight abduction where you wake up tomorrow and they are just gone... There will be Flash games and site components around well after the technologies have been replaced. So there is no harm in learning flash, and will do nothing but help you as a developer, but for looking to the future of mobile games the answer is HTML5 and JS. For an idea on what Adobe is doing, check out the Preview of Edge. Hope that Helps. 