I've developed a couple of WebGL games, and am trying them out on Android. I found that they run very slowly on my tablet, however. For example, a game with 10 sprites or so runs as 5fps. I tried Chrome and CocoonJS, but they are comparably slow. I also tried other games, and even games with only 5 or so moving sprites are this slow. This seems inconsistent with reports from others, such as this benchmark. Typically, when people talk about HTML5 game performance, they mention well-known and higher-end phones and tables. While my 7" tablet is cheap (I believe it's a relabeled Allwinner tablet, apparently with the Mali 400 GPU), I found it generally has a good gaming performance. All the games I tried run smoothly. I also developed an OpenGL ES 2 demo (in Java) with 200 shaded 3D objects, and it ran at 60fps.
My suspicion is that the WebGL engines have unacceptably limited support for many low-end and white-label devices (for example, relying on software fallback for no apparent reason), which means there may be a large section of gamers you will not reach when you choose this as your platform. I've heard rumors about inconsistent performance of HTML5 and WebGL on different devices, but no clear picture emerges.
I would like to hear if any of you have had similar experiences with HTML5 or WebGL, or whether I can find information about the percentage of devices I can expect to have decent performance.
EDIT: As a "thorough" way to prove my point, I've started on a WebGL implementation of my own, to see if I can do any better than CocoonJS. Results are promising so far. On said tablet I can draw like 10,000 sprites at 60fps, all updated and drawn in JS through a WebGL compatible API. Check out the APK here. So, I guess that proves that the existing WebGL implementations are really doing something wrong. I'm now in the process of making my games playable in my framework.