"A well informed source on IRC sent me 2 sreenshots, which demonstrate a new unnannounced feature in the new version. In the two pictures there is an In-Game-Demoplayer in the coming HL/CS version that will allow you to rewind, run in slow motion and also demo editing from within the game. "
From the looks of that its big changes to HLTV. Also in the first shot it seems the framerate limit has been removed. (118fps).