Why movies fail; 1) Poor dialogue
Was this movie TOTALLY based on impov? That is what it seemes like to me, I find it hard to believe that they followed a written script. If it was based on improv, this movie shows you the dangers of letting actors have free reign in a scene when they really have nothing to say. The dialogue (or imporv scenes) were so poorly constructed that the writer of the book must have been tearing his hair out. Compare this movie to 'The Maltese Falcon' where every sentence carried meaning, you see what I am getting at.
While the acting was good and the directing competent, the viewer needs good dialogue for a movie of this type to grab you, Eight Million Ways to Die just did not have that.
The thing is, this movie had potential, take away the lame ending and add a good writer to give the actors some tight dialogue making sure they follow the script, add few new action scenes and you might have a winner.