They fixed the ludicrously random hit detection, they standardised the tick-rates (which affects Rate-of-fire, speed, reloading etc, ensuring a more even experience cross-server), they’ve also improved the netcode. They’ve included over 140 achievements to the game too
A number of people are not happy about it. Complaining about EVERY aspect of this update. However, the only two valid complaints I’ve heard so far are that 1) clamping everyone to a 66-tick will kill competitive play and 2) the engine update has ruined peoples FPS.
As 100-tick was the norm, and it was the only way to play without lagging so much that when you peeked your head out you’d get shot. Valve assure that the new netcode will offset these problems. However, logic never quelled a howling mob.
Also, since they’ve updated the game engine, and basically DirectX 7 is no longer supported, which means that people on really old PCs have experienced a slight FPS drop. This is a semi-serious issue. People with the same-spec PC are now jittering and juddering.
Remember though, that a computer that can’t handle Direct X 8 was likely created around the time when Windows 98/2k was the norm. Sure, they may have updated the OS to XP but come on, your FPS dropped a little, and you can still drop the quality slightly.
Most of the crying on the forums besides these technical issues are in the form of “I don’t like the interface” or “Achievements suck, this is a game for babies now”. Firstly, 90% of the new interface elements can be reverted to the old form (like the server browser, netgraph etc) and although there’s no option to revert the scoreboard, it CAN be reverted back using some magical hacks.
Now, normally I only play CS:S at lunchtimes, and so far I’ve found it to be just the same as when I played it the day before. Okay, a few mods hadn’t been updated, but by the evening the servers I usually play on were back to normal. There are a number of other bugs thrown up by the update too, but Valve are Valve, and I give them the benifit of the doubt that they’ll fix it in a few weeks.