Enough reasons to build games but most of it, it is very fun to do. Most people believe that HTML5 will replace Flash if it comes to online gaming. Mobile and social gaming are very hot right now. With HTML5 the possibilities on the web are very big also for the gaming industry. So here are some frameworks that will make it a lot easier to develop HTML5 games.
EaselJS comes with a MIT license and is a part of createJS suite which also contains TweenJS for tweening animations, SoundJS for playing sounds and PreloadJS for preloading your assets. It’s easy to learn and has good documentation with good number of tutorials available on the internet. As it’s inspired by flash/AS3, flash develpers will find it easier to adapt.
RPG.js is a HTML5 Game Framework focused on building 2.5D Zelda Bitmap-based Role Playing Games. The framework uses EaselJS a utility knife of sorts for working with the HTML5 Canvas Element.
Panda.js looks like a neat JS Game Engine featuring a Canvas/WebGL Renderer, Physics engine, Particle engine, Tweening, Sound Manager, etc. It also plays nice with mobile/touch interfaces.
Isogenic Game Engine
If you’re building an isometric RPG, this is the game engine for you. It comes with just about everything to support a realtime multiplayer game on the client side and backend (node.js) with both sides running the same codebase.
PuzzleScript is a simple, open-source game engine by Stephen “increpare” Lavelle that allows you to easily create turn-based puzzle games using a unique scripting language. The engine is HTML5-based and games can be built and shared (along with their source code) straight from your browser. The graphics, which are composed of 5×5 tiles, are also designed within the editor, in the same manner that levels are defined.
Cocos2d-HTML5 is a port of the popular Cocos2d (and Cocos2d-iphone). It is primarily used for mobile-first games.
LibGdx is the most simple to learn of the frameworks, and is in a way the most complete: it supports Particle Systems, Tile Maps, Box2D, 3D objects, Fonts, UI elements, among other things… And it is the most optimized OpenGL framework/wrapper you will find anywhere.
Pixi.js is a devoted 2D rendering engine that taps into the power afforded by webGL with Canvas fallback. This means that people can create content once and serve the same code to all platforms.