Taisei (as well as Touhou series) is a 2D vertically-scrolling danmaku (bullet hell) action game, placed in a fictional world of Gensokyo. The goal is to escape from hundreds of bullets. Touhou series originally began in late 1990s by a developer called ZUN for PC-98 and, later, for Windows computers. Development of Taisei (previously OpenTH) started in 2012. It is written in C, OpenGL and SDL, contains ~100k LoC, and supports Windows, Linux, Mac OS and Web.

What I like about this game is, that Taisei Project has soundtracks in the wild (by Tuck V). It also features fancy graphics (colour blending, shaders, character drawings). Not to mention, this game dives deep into the gameplay and realm, and is pretty hard in the beginning (as virtually all Touhou-ish games). Have fun!