One of the reasons I became so obsessed with the original Counter-Strike was the absolutely ridiculous number of player-made, unofficial maps. The problem was, the good ones were few and far between, and there was no real way of weeding them out. Now, with the launch of Maps Workshop in Counter-Strike: Global Offensive, that little problem will be solved. Ah, there you are fy_iceworld, my old friend.
As of right now, the Maps Workshop hub has a lot of maps that were popular during the days of the original Counter-Strike and Counter-Strike: Source, but with the new, easier to use map creation tools, I suspect we'll be seeing a whole new wave of really cool battlegrounds. You'll be able to find all of them in-game in the in-game map browser.
Check out this post on the Steam blog to find all the information you'll need to create and upload your own custom maps.
Oh, and Valve has added cs_assault to the Classic Maps rotation. I've missed that map, too.
