Source vs Superpowers

Valve's official documentation website is great for newbies. It demonstrates the pros and cons of the engine (and since the website isn't maintained by Valve, but instead the community, the pros and cons are largely unbiased). There are also a number of pages dedicated to entities used within official Valve games and also community-made mods that were turned into full-fledged games by Valve. These pages explain the ins and outs of how most source programming works. There are also guides for Valve's tools which are both included in Source SDK and in any Valve-developed game.

Since it has precalculated lighting, this engine is great for low end PCs too.

You don't need to code your own door or ladder etc. You can pretty much use every entity used in Half-Life 2 yourself easily.

Of course you can program stuff into source but for level design only, source has a really easy input/output system for your level logic (e.g. doors, trigger when player walks into room...).

Source includes Source Filmmaker, a video capture and editing application.

You can spin up a server and work with other people at the same time.

This isn't a 3D with 2D on the side type of engine. The scene-editor supports both 3D and 2D views, allowing ease of use no matter what type of game your making.

The community can develop and release their own plugins to add additional features making game development easier. All of these plugins can be easily downloaded in the app.

It's got a scene-editor, cubic-model creator, text-editor, 2D image / animation importer, and a very useful tile-map editor.

Games can be published to the web with good performance, and the game-framework utilizes TypeScript to make programming games a little bit nicer.