Harry didn't die because he was the true master of the eldar wand, it having passed from Dumbledore to Draco to Harry, thus when Voldemort 'killed him' the only thing it was effective agaisnt was his horcrux, Harry thus was given the option to return.
The book makes a point of explaining that Harry's sacrifice gave the same protection via the same method his mother used on him to everybody, thus voldemort was unable to harm anybody (as happened in the book) and his spells were inffective against Harry due to Harry being the eldar wands master.
Harry was getting his backside kicked in the film was classic hollywood crap, the book portayed Voldemort as being completely ineffectual during the ultimate fight and Harry explained to him why during the duel before killing him in front of everybody.