[Zero]

for me personally the film has to be 'engaging' or i totally shut off and start counting the ceiling tiles in the roof of the theater- or the lights or curtain rings, or whatever (honestly, i really do - it annoys my friends to no end as i'm craning my head backwards to get an accurate count)

i think the key to engaging is the characters in the film. if i 'like' them or at least 'believe' them, then i'm willing to go just about anywhere - but if i find them unbelievable, i'm counting tiles. also, i hate when films violate their own logic - i.e., when everyone says - "oh they way to kill Freddy is to do this" then they do it and it doesn't work (but not for any good reason, just because they don't want to end it that easily). this is why i find most 'timetravel' movies really annoying - they almost always abandon the premise and, as we'd say in the states, 'punt'.

(i'd also say i find this problem at work in some of carpenter's films, where he seems to give up on a premise and just find a resolution)