I played 1.6 competitive and when Source came, we already had lazy days in the team. We decided to switch to Source and just... play it... still competitive but more on a fun basis with less training, playing the little leagues and cups. Source is fun, looks better than 1.6, less pain on the eye but it takes less personal skill too. Not necessarily on tactics and teamplay, nor on reflexes and long range shots but everything close quarter rewards spray 'n pray way too much. And the netcode issues at the start of Source killed it too. Not playing the expensive tick 100 server was pain in the ass... those starting problems killed Source before it even had a chance. Valve screwed themselves developing server patches at Valve time.
Otherwise Source could have been great for CS...
Haven't touched CS for years, even with my old clan buddies we play other games from time to time. Afaik none of us got GO, not even tried it once.