the directory is in steam\steamapps\[your username]\garrysmod\garrysmod\addons - you put the folder in there, at least for mods. Not sure about maps.

I can reccomend the Wire mod, if you have some (fairly basic) electrical knowledge.

take every key you find :) It may come in useful sometime. As a matter of course on quests I take the keys of those involved ...

It's saved me a fair bit of time in many quests.

Some shooters do play well with special powers but some completely suck, the likes of preys spirit walk and death walk are complete crap, and goldeneye rouge agent (old i know) is utter rubbish, some games do work well though such as...Maxpayne, Matrix path of Neo etc...Samfisher_1

 oh gosh yes. I hated prey. It can work well in some games though, while I think FarCry went off the rails with feral stuff, I think the bullet time in FEAR is quite cool.