Right, long story really though.
A company took over from Valve (forgot the name), after noticing the flop for CS:S ESports in comparison to 1.6. They took out some of the big bugs/competitive gaming killers. Such as, bunny hopping (feel free to watch Phoon on youtube for an example), crouch bugging (tapping ctrl to see whats behind a wall/box and not appearing to anyone behind the box), **** lack of recoil (people were *wasda*ing; running about while spraying too much in comparision to 1.6), **** interpolitation(SP) (it's the sync between you and the server - if you have a tight interp it will force update from the server whereas a slow interp (100ms) will 'predict' where the player is between updates leading to not so accurate hitbox mapping)
Few more minor bugs too, and map development (as most maps were too CT sided for competitive play).
Most bugs I mentioned above were fixed by firstly being introduced to the beta, then being rolled out. The updated maps were released but pulled shortly after; not sure of the reason - but will likely be reintroduced soon.
A recent update has ruined CSS for me though, they've changed recoil patterns to mimick CS1.6, but they've left a few bugs in. For example, you can QQ (switch between weapons) and it resets recoil. Also they've completely messed up interp. And now you can find yourself getting killed while being "behind a wall".
I'm making these issues seem much more serious than they are. But they're stupidly important when playing competitively. And it's likely you won't even notice when playing public.
Inbox me any questions if need - rarely check old threads.