Josh, I just might have to side with Bel here. A lot of stunts seem unrealistic, but make for entertainment.
I think of the "Dukes of Hazard" type of movie, and you have to ask: How many times can a car make a "jump" over a ditch and land as hard as that car does? Real life answer: Once, if then. After that jump, the frame and the suspension are toast and the car is going to be scrapped. They go through a lot of cars shooting a "Dukes of Hazard" show.
To be truthful though-- I have to ask: Did you go into the movie looking for "realism" or "entertainment"? Sure, the big American cars do impossible stunts and have incredible wrecks-- but that's part of the movie, not real life. Eat your popcorn and enjoy the movie.
What would happen if a large asteroid slammed into the Earth?
According to several tests involving a watermelon and a large hammer, it would be really bad!