The specific changes include:

CS:S
- New map: de_inferno
- New map: de_port
- Updated Counter-Terrorists player model with new headgear and color scheme
- C4 red flash displays properly if the bomb is planted under water now
- C4 explosion damage is no longer affected by water
- When a map is loaded, an associated .cfg file is automatically evaluated. This cfg file must be located in the cstrike/maps/cfg folder and be named [mapname].cfg. For instance, the file cstrike/maps/cfg/de_dust.cfg will be evaluated when the map de_dust is loaded. This is useful for per-map rules, bot rosters, etc.
- Added new route to roof of hostage shack in cs_compound, and improved bot navigation in the map
- Players must now target another player for at least a half second before the player ID text hint shows up
- Grates/chain link fences no longer affect bullets
- Counter-Strike player ragdolls are now affected by ragdoll magnets
- Fixed a bot crash caused by finding too many hiding spots in a region
- Bots no longer attack enemies that are very far away unless they have a sniper rifle, or the enemies are shooting at them. Instead, they track the enemy and move to a better attack position
- Bots understand +use doors now and will pause to open a door before continuing through it on their way to whatever they were doing
- Bots use less CPU now, especially when in combat with far away enemies
- Extended the syntax of the bot_add, bot_kick, and bot_kill commands to also accept "t" or "ct" arguments.
- Fixed bug where bots would stop and become unresponsive if they wanted to hide in an area with no hiding spots
- Improved bot navigation on the windows and ledges of cs_italy
- Fixed recording value of cl_interp in demo files and restore value during playback

Source Engine
- HTTP downloads from the game server system support downloading .bz2-compressed files
- Disable old style (non-challenged) server queries by default (use the sv_enableoldqueries cvar to change this behavior)
- Added cvar tv_delaymapchange to delay map changes caused by frag/time limit until the whole game is broadcasted via SourceTV
- Fixed lag compensation invalidating bone cache for players moved back in time.
- Fixed lag compensation interpolation error between 2 ticks

Half-Life 2
- Fixed some NPC actions not being properly randomized
- SourceTV (part of the Source Dedicated Server)
- Fixed memory leak in relay servers by releasing receive tables correctly
- Bandwidth output in tv_status in kB/sec rather than bytes/sec
- Running a new map command (spawning a server) shuts down TV relay in same process
- Fixed SourceTV chase cam following ragdolls of dead secondary targets