Gmod? Pros and conss?

I have Gmod. Left 4 dead 2 doesn't count as a source engine. You have to buy Half life, Half life 2, Day of Defeat, Anything made from Source. To get weapons and contraptions that you speak of, theres a website for gmod where you can download maps, weapons, different contraptions as well. Lots of Fun stuff. Gmod is fun because of the freedom that the player gets. Multiplayer is fun, play with others and show off your skills of building or just messing around and acting weird. Fun game and I strongly recommend it. I hope this helps.