Should I buy GMod

Yes man, If you living in EU or America Region, You must BUY this game, It's still worth it, but If you living steam minor country, I must not use your money useless way like this

if you have friends to play with then its pretty fun. so probadly no, lol

With friends it is going to be great, without any then no

GMOD is such a versatile game and I definitely suggest getting it just to have fun there's so much opportunity.

garrysmod is fun with friends and by yourself. If your not feeling a specific gamemode theres plenty more to choose from.