Garry's Mod online is an experience i cannot describe.
Offline, you can do whatever you want, literally and the addons make it all the better.
Now when you have friends together that can do whatever they want and i mean ANYTHING, it can get quite epic. Like that pic in the LMAO thread i just posted.
Is it worth it? I lanned the game with a couple of friends a couple years back, and I wasn't really fond of it. It was alright for about 10-20 minutes, then I got bored.
It really depends on what you do, i was making videos a while back and i had a blast.
If you just rush into it for your first time, of course it's going to be boring, but eventually when out learn how everything works, you can waste many hours in this game.
You might see me pop in there some time. I love watching Garry's Mod videos on Youtube, I've always wanted to make one. Just never took that first step, even though I have it.