Considering the setting of the film, they did a considerable job creating incidents; however the storyline didn't seem plausable.
1-Nobody would have taken that long to discover there were extra tools with him the entire time or that there were holes in the coffin.
2-He found a knife but never attempted to cut throught the wood or pry the nails out?
3-"MAKE VIDEO!" "MAKE VIDEO!" He complied with terrorist demands? Why? Did he think they were going to dig him up to punish him? His family wasn't in danger, have local police come get them.
4-His lifeline on the phone wouldn't have argued ideological differences with him.
The main character spent very little time actually trying to get out of the coffin; instead resorting to countless, frequently pointless phone calls. He seemed inept, which is fine for other characters, but when your life is on the line it makes the main protagonist unlikeable.
The most fun I had watching this film came from making fun of how bad it was.