When comparing Microsoft XNA Game Studio vs Gosu, the Slant community recommends Gosu for most people. In the question“What are the best 2D game engines?” Gosu is ranked 52nd while Microsoft XNA Game Studio is ranked 81st. 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 Easy assets
it is very easy to import your own 2 dimensional assets

Pro Very easy to use
relies largely on drag and drop elements and has been used to create notable high quality 2d games such as DLC Quest
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 It's dead
It is not getting updated and Microsoft does not recommend using it anymore.

Con Limited platform support
Only supports Xbox 360, Windows and Windows Phone
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.)
