You never lose the aim (unless the mechanics change, but with CS there have only ever been minor changes), but game sense starts from scratch again with GO there's so much more complex plays than before due to better smokes, use of molotov etc.
I really love it though. The match making system is so much better than logging into mIRC and trying to get a 5v5 with someone else having a server, you can just jump straight into a game.
You soon pick it back up as well, I started as single AK rank (master guardian) which is pretty dire but in two months I'm already and badge rank (DMG) and hoping to get to Legendary Eagle soon!
The only bad thing about the game is you get some complete w*****s playing it, but once you get some mates who play it, it's awesome!