You're all insane :P
Just decided to check out the forums for this film, even though it's been several years since I saw it the first time.
All you naysayers are insane. Lost Souls ranks in my top 3 for favorite endings. The countdown... the pause... the shallow breathing... the sign flashing the mark of the beast... their eyes meeting... that VERY EERIE SMILE on Ben Chaplin's face and the quick decision to kill him right then before it was too late.
My God, what's wrong with some of you? That smile alone is worth seeing the film for. Why? Because Ben Chaplin pulled it off SO perfectly. The time was upon them finally, and Peter looked himself over and gasped and tried to tell Maya that it was still him, that nothing happened. BUT THEN...
...this is the moment of cinematic magic -- that pause as they're regarding each other. Maya is just studying him, waiting for some indication that the transformation had actually occurred. And the devil cracked! The clock flashed 6:66 and his expression of "It's still me, it's Peter" totally cracked. It was a staring match between Maya and the devil, and Maya won.
Amazing. Love it, love it, love it.