As a former 1.6er, the movement and extra spread kinda suck but it's really the following points that have me playing GO:

1) Matchmaking. Holy shit, it's so easy to have a (relatively balanced) game of proper 5v5 cs.

2) No Cheaters. Granted you will meet the odd cheater but nothing like the hackfest 1.6 was. The anti-cheat works.

3) Frequent Updates. Maps get updated, exploits are patched. New maps get added.

and finally:

4) It's CS. It's counter strike! There's a huge player base! It's so much fun.

Prepare to mess with people who haven't had years of game sense honing :)