Strikes a pretty perfect balance between the simplicity and focus of something between Pico-8 and Picotron, and the flexibility and BYO-tooling of Love2D, with the same spirit of convenient API design as something like DragonRuby GTK.

Probably the best way to describe it is "Pico-8, but you can change the resolution, expand the palette, 

The ability to "loveify" your Usagi project into a Love2D project is a nice touch and way to say "don't worry, you're welcome here but we've also got a pretty reliable backup plan ready for you if you need it".

The "Book" docs are great. The Shmup tutorial was also quite useful and gives you the foundation to make a full retro-style shmup. There's a bunch of other recipes. And there's also sections dedicated to transpiling to Lua from other languages. Speaking of language support, automatically generated LuaCATS type declarations are extremely useful too, it's like "JSDoc types" with the TypeScript LSP but for Lua. I found the default Zed Lua LSP was pretty snappy with them and I had a typesafe project pretty quickly.

Overall a great package. Has its limitations (mostly intentional, to put prototyping workflows first and foremost), but a solid engine in my short experience.