Gamespot has an article up about games that were MIA at E3 this year. It seems that quite a few games were expected to be shown, but were markedly absent, STALKER being one of them.
Though the absence of Duke Nukem Forever was expected, the absence of
another top PC title was not. S.T.A.L.K.E.R.: Shadow of Chernobyl was
nowhere to be found at THQ's booth, despite the fact that a gameplay
trailer was featured prominently at last year's E3. Though the game has
been in development since 2001, its 2006 release remains tentative.
It seems that STALKER wants to join the vaporware club.