So, my take on the plot is: Earlier in her life, Beth (Hall) was in an accident and briefly "died" before being brought back to consciousness, but not before seeing that there was nothing on the other side. This nothingness left a void in her life, which she managed to fill by getting happily married. However, 'Nothing' (the grim reaper?) is none too happy that Beth escaped death and so he feeds "urges" into her husband in an attempt to get him to kill her. Her husband tries to deal with these urges by finding women who look just like his wife and killing them, in hopes that Nothing will be fooled into thinking he has murdered Beth and thus leave them alone. However, Nothing isn't fooled, so the husband finally decides to kill himself, believing that Beth will now be safe. However, Nothing continues to come after Beth, trying to push her to the brink of insanity and suicide. In the end, Beth is brought back from the dark side through the love of her best friend, who arrives just in time to save her.

Another take on the story could be that Beth is just a severely depressed person who was imagining all the weird stuff that was happening because she couldn't deal with her husband's suicide. So, the whole story is mostly just happening inside her head and not be taken factually (ie. her husband isn't really a serial killer).

I was afraid for a moment that this was going to be one of those movies where it was revealed in the end that Beth had actually died for good in that earlier accident in her life and that this whole movie was just a Jacob's Ladder-type scenario. Glad they didn't go down that path.

She's kind of a jerk to everyone. Her husband turns into a serial killer in order to try and save her.
Some of the ideas were good, like the mazes and the 'women who look like her' to throw off the 'nothing'. In the end, though, her husbands efforts didn't really matter since the 'nothing' could just grab her and smash her into a wall anyways.
Also, her seeing other women at different times when dreaming didn't really make sense.

"nothing" spirit. How Beth would see a ghostly outline, but when she moves the outline is revealed to be formed from the borders of other things (the "nothing spaces".

She thought it was a demon/entity guiding him. I thought he was suppressing urges to kill his wife by killing similar looking women.

Final Destination for adults.