The acting aside, the premise is one that really makes you think about the consequences of the decisions we make and how fate might act if we really could affect what has already happened.
I grew up reading the great sci fi authors - Asimov, Niven, Clark, etc. and I always loved the stories about the paradoxes and dilemmas involved in time travel and trying to affect what has already happened.
So all the irony in the plot really overcame the less than perfect casting and screenplay and made the movie interesting to me.