I saw that movie by accident at my boys house, we didn't even know what it was called at first...it is soooooooooooo creepy and twisted with the plot...the resolution at the end just makes you feel dirty...I mean to the point where I didn't even want to use HIS elevator when I was leaving his house...and it still creeps me out when I go over there, I stick to the stairs.
I mean, the premise is based around Karma and ultimately having to pay the piper for the wrongs you commit in your life.
Overall...wouldn't see it again, but if you like creepy movies where people get arbitrarily killed...go for it.
Recently I saw, The Girl With the Dragon Tattoo, The Shawshank Redemption (again) which I love, and Taxi Driver (classic)