When comparing Codea vs Gosu, the Slant community recommends Gosu for most people. In the question“What are the best 2D game engines?” Gosu is ranked 50th while Codea is ranked 107th. The most important reason people chose Gosu is:
Gosu is not a game development framework, only a media library that happens to be suited to game development. (Kind of like SDL in the C world.) That means the interface is relatively small.
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Pros
Pro Helpful code editor
Errors show up live, as you type. Smarter autocompletion picks up your local and global variables, including nested types. Everything else is just plain smarter, from indentation to highlighting.
Pro Ships with music and sound packs
Codea ships with three great music and sound packs, composed just for Codea and free for you to use in whatever you create.
Pro You can code on an iPad and easily distribute the game
Pro Location library
Location library lets you make use of the GPS inside your iPad. Get your latitude, longitude, altitude and more with a dead-simple API designed specifically for Codea.
Pro Lightweight
Gosu is not a game development framework, only a media library that happens to be suited to game development. (Kind of like SDL in the C world.) That means the interface is relatively small.
Pro Mature API, actively maintained and developed
Gosu has been under development since 2001. It is mature and has several toolkits built on top of it to provide additional functionality.
Pro Cross-platform, even mobile, using Ruby
Cons
Con Deploying Ruby apps is a mess
Games built with the Ruby to .exe "compiler" do nothing more than extract your source code and Ruby.exe to %TEMP%, then run it. The code is not really compiled at all. The process for wrapping games as Mac apps is a bit nicer, but you'll need a paid Apple Developer subscription to code sign the app, or users will see a warning/error when running your game.
The only way to really compile Ruby is to use RubyMotion, which does not work on Windows and requires a paid subscription on top of the Apple Developer one.
(This Con is not specific to Gosu. Deploying Ruby code has never been fun.)