The first Paranormal Activity film was the first horror film I screened during which members of the audience actually fled the theatre, (obviously from the big boo scare at the end.) I said when it came out that if you didn't stay until the very end you would probably think the film sucks. The entire film was build up for one big boo scare. Sure the majority of the film suffered for it, but I thought the payoff was decent enough. Could the payoff have been better? Certainly, but the one they went with did the job nicely.
As for my avatar, nice you recognised it.
I was initially going to go with the original film (photo), but I figured this drawing I found would be less disturbing to people on these forums that aren't as keen on gore as I am.