Trying to get into the game

I'm detoxicating from League of Legends, and getting more into singleplayer games, and really open-ended multiplayer games like Warcraft 3, and Minecraft.

Recently, I've joined this forum, and saw the really active community of Garry's Mod players.

Do you guys think I should play this game?
Why should I play this game?
Is there anything I should know before investing time in it?

Help me out, guys.