The fact is that 1.6 is far more realistic and fun.
In Css you can win just by spraying round after round.
Try that i 1.6.
i completely disagree with this comment
i started playing CS in 1.5 and loved 1.6 when it was updated and played it until source, then played source and have gone back to 1.6 here and there...but ya heres the things i've noticed.
the spray in 1.6 is actually FAR more controllable. you can easily just scroll your mouse down and hit basically the same area with all your shots. the recoil is a lot worse, but its so easy to control its ridonkulous. in source when you spray, after about 3-4 shots it seems that your bullets don't exist anymore until the random CSS headshot that all the 1.6 ppl whine about. well its simple, kill him before that happens, you have about 1.5 seconds to do so.
also one of the biggest complaints in the conversion from 1.6 to source, for the 1.6ers was that people can still move in source after being shot. they are slowed down but can still move...which made it hard for 1.6ers because the fact is in 1.6 if you are shot you glitch and cannot move. therefore you basically shoot a guy once and hes yours unless he pulls off a fantastic whip around headshot.
i know not many others will agree with me, but i think source takes more skill to master than 1.6. actually when i go play 1.6 now (well when i used to go back and forth) i'd take about 15 mins to get used to it again and be completely pwnage.
also the sounds are a lot louder in 1.6....very easy to tell where ppl are.
edit: forgot to mention - try looking at local electronic stores for used games or even pawn shops. most big companies won't sell old games.