Is the game worth purchasing?

Y E S
i have 400 hours and i have gifted it to many friends because it is that fun

This game is very enjoyable, and while it does show its age, is fun and customizable almost everywhere. For only $10 USD that's the price of a burger or a reusable mask.

Is there a guide for this game?

Gmod gets all it's power through mods, modding community and having fun with friends. It's a game where you can do everything (if there's a mod for it). If you have some friends you can try if you want

bruh im also thinking of getting it too

Naturally, because there are a lot of modes in it and most often a fun community

yes i think this game is fine with addons and servers

You should 100% if you are into Sandbox games.
You can get so much playtime from just playing only singleplayer with mods.

Yeah it's pretty timeless and one of the funniest game to play with your friends

yes due to the endless possibilites