I can describe the movie in one word: Awful.
Problem the first: Suspense scenes are way too drawn out. After awhile the viewer will feel like screaming "Expose them or let them escape! The scene's gone on long enough!"
Problem the second: The act structure makes it feel like the initial cut of the movie ran too long (And since this is a 2 1/2 hour movie, that's saying something) and the director needed to cut out all transitional and character development scenes, leaving behind just the major events.
Problem the third: The notion that an officer who is loyal enough to fly into a rage and strangle a mole with his bare hands for treason would then turn around and betray his country to the mole's associates before the body is cold.
Problem the fourth: This is actually two stories, which do not mesh well together, being turned into one movie. Only one major character is relevant to both stories. The only thing they have in common is they both end with destruction in a certain theater on the same night. The title characters are actually in the story with the least screen time.
The film would have been much better if the stories were separate films: One movie, a violent comedy, about the Basterds, a Jewish-American Commando unit sent behind enemy lines to commit atrocities and demoralize the enemy, and the Nazi's efforts to stop them. The other, a drama, about Shoshona, a French Jew who escaped execution by the SS and became a theater owner under a new identity, only to find herself unwillingly courted by a German war hero and ending up with a perfect opportunity for revenge. If you need allied soldier-types in the second film, add a French Resistance cell that thinks Shoshona is a collaborator and wanting to strike a blow against Germany by killing a famous sniper and his presumed mistress, only to learn that they hold back for a time, a much wider selection of targets will present themselves.
Don't buy. Don't rent. Don't watch.