A post has been made on the GSC Game World forums
by Oleg Yavorsky in response to rumors of the game being cut down.

Rumour 1. S.T.A.L.K.E.R. had been turned into corridor-like scripted shooter, while A-Life was removed.

Yes. After playing Serious Sam 2 we decided – "why should we bother implementing that A-Life" – let's add more gore and 'stiff' scripts as the player moves alongside the 'corridor'.

Just kidding.

Thanks ShackNews