At least Phone Booth and Panic Room has something going on in their surroundings. If this movie only focuses the inside of the coffin and nothing else then I couldn't imagine whats it gonna be like watching it.

Also just watched it a few days ago. Glad I didn't missed it. Its been a while since I last cared for a character.
You can really feel for the character. The last few minutes was just so intense and then WHAM it hits you like that with a shocker. I was like "WTF MAN NOO!" when the guy on the phone said "I'm so sorry."
Feels good to finally see a good movie without the usual endings.
Theres a scene after the credits where the camera focuses on the word "Mark White" which was written by Paul in the coffin. I'm not sure whether its supposed to send out some hint or message but yea.

I guess I'm lucky not to have watched it in the cinema otherwise it might have been spoilt by those who keeps complaining.

I've watched both and they're nothing alike. 127 Hours was slow and boring. The whole movie was kinda calm and you don't really feel the rush to save the guy until he starts cutting his arm.