Should I buy Garry's Mod?

Definitely. It is by far the most flexible and fun game i have came across, since the creators actually encourage user made mods and addons, theres always something new to do in gmod, whether you make your own gamemode, map, addons, or even just play others creations, i have yet to get bored of it.

If you have some friends, the game is worth it.

It would be very interesting to call your friends and enjoy the game together

There are many active groups on gmod...but its true only some gamemodes are popular. Gamemodes like TTT are only active in some regions like EU.
So, play with friends like other people have said.

Garry's mod this good game, with a lot of gamemode buy it

It's the best game of the world, you can do wath you wan't with a good community

It's worth it. There is so much you can do on the game

If you can play with friends it can be super funny game. If you play solo, don't but this.

Yes, Gmod is great sandbox with a lot cool features like workshop and servers. But mostly 40% of servers are trash. Sadly

Of course, if you're a fan of half life 2, then this game should tighten you

Garrys mod is one of my favorite games I have ever played. The fact that there is so much replayability and tons of variety then it means you should buy it.