This morning people at GDC were shown the fist in-game footage of Killzone 2. Sony has previously stated that Killzone 2 would not be shown at GDC however were treated to this earlier than its expected E3 2007 debut (itís also been confirmed that more of the game will be shown at E3 2007). SCE President of Worldwide Studios Phil Harrison advised attendants that they were showing this footage as "an example of our technology" and that they "shouldn't think of it as looking at the game directly." IGN describes the footage as "both ISA and Helghast soldiers blasting the bejesus out of each other" noting the aftermath as to be like ""BLACK" for the next generation."
Killzone is being developed with the "Playstation Edge" which includes an RSX performance analyzer for optimal GPU performance. According to Billy Berghammer of Gameinformer magazine "The environments showed quite a bit of destructible elements, as well as some impressive lighting" but he also stated "itís definitely far from the initial trailer that the company initially showed".
My Guess about how the footage actually looked (considering nothing has been leaked)? The Killzone pre-rendered trailer compared in-game is most likely similar to the Motorstorm pre-rendered trailer comparison to in-game. I do believe that graphics done to spec based on CGI trailers is a good way to develop, but nothing can ever come close to CGI.