Good luck memorizing the path and name of every model in the game and memorizing every command to make a simple weld.
You missed it
badly
I can open up l4d and copy and paste some commands I get online into the console, or better yet download one of hundreds of mods that lets me spawn misc objects. You can use the console to spawn zombies at will or turn them off, and just mess around g-mod style in noclip lighting the skybox on fire or whatever. That is what gmod is at its core, and only minimal expertise is required. Sure you can't easily get the tools that are programmed into gmod, but if that is what you are focusing on then silly.
At audiosurf's core is pretty much just challenging your hand-eye coordination on a challenge based on your own music. I can't imagine this being easily replicated in g-mod, and if someone does, they are probably a gmod wizard. I could be wrong since I can only gmod well enough to do poses and crappy car things.
Anywho, I would reccommend gmod if you have some friends that play it actively, but if you are going to play on your own, go for audiosurf.
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