The short review: this is Tarantino's least successful film. But because it's Tarantino, it's most likely better than most of the movies you've probably seen this summer.
There are several quite wonderful scenes, and some standout performances, mainly Christoph Waltz as Hans Landa, the weirdly fey SS-Officer-From-Another-Planet, and Melanie Laurent as Shoshanna, the young Jewish survivor who hatches a plan to kill all the German top brass during a film premiere in Paris.
If Tarantino had just stuck with the Shoshanna story, he would have made a successful if not spectacular film. There would have been plenty of tension, Shoshanna and Landa could have exchanged geek trivia about prewar German cinema while subtly maneuvering toward their respective goals, and then there would have been a blazing and satisfactory finale.
Unfortunately Tarantino also decided to remake The Dirty Dozen, and therefore we meet the Basterds, a group of Jewish-American guerillas parachuted into Nazi-occupied France with the avowed intention of scalping 100 German soldiers apiece. The Basterds are led by Brad Pitt, who is given a bizarre accent that undercuts his character, and who is apparently told to spend much of his time making strange frowny faces.
The odd thing is that Tarantino really couldn't think of anything to do with the Basterds. He already had his wiping-out-the-German-brass story, so by the time the Basterds come along with their completely independent plot to kill all the Germans, they're redundant. Shoshanna's plan is sufficiently comprehensive that the Basterds aren't necessary to its execution.
Many of the scenes in the film are excruciatingly overlong, especially the one in the cellar, which went on so long it threatened to become a movie of its own. The structural function of this scene in terms of plot is to take three Basterds out of the picture, which means Tarantino has three fewer people for whom to find things to do--- which by that point must have relieved him considerably. (The actual Dirty Dozen film found something important for each of the dozen to do during the course of the movie. Tarantino couldn't manage that.)
The Basterd plot is, basically, ludicrous. A real group so constituted wouldn't have survived 48 hours in occupied France. This isn't a fatal flaw, because the Basterds live in a very cartoony world, which isn't about the real Second World War but about a lot of cheesy movies about the Second World War. Tarantino's films are geek-fests about other films. If you didn't know 1970s chop-sockey films, you missed half the point of Kill Bill.
The main problem with the Basterds is that they spend most of the movie stumbling around accomplishing nothing. Shoshanna's story doesn't need them--- Shoshanna and Pitt never even meet. The Basterds contribute nothing to the outcome except to add a little comedy and a little extra mayhem.
And there were some moments that disturbed me.
It's been obvious for a while that Tarantino likes to bruise, batter, bloody, torture, and kill attractive young women in his movies. (Kill Bill. Death Proof. QED.) Basterds is no different. The sadism quotient in this film is pretty high.
Which brings us to my big problem, which is that in this movie, the terrorists are the good guys.
The Basterds are explicitly terrorists. They exist for the sole purpose of terrorizing Germans. They torture, beat, and brutally kill their prisoners, and they enjoy it when they do. They say they are killing "Nazis," but their prisoners could have been Ukrainian conscripts for all they notice or care.
(Yes, real-life American soldiers killed prisoners. Yes, the Basterds are a guerilla outfit and can't walk around the maquis with a bunch of captives. But executing prisoners is a little different when you torture them first, isn't it? A bullet in the back of the head is different from being beaten to death with a baseball bat, isn't it?)
Torturing and murdering prisoners is an essential part of Basterd cool. We're meant to admire them for it. This is a film that states explicitly that American soldiers are terrorists and then congratulates them.
And no, I didn't see any irony in there. I didn't see any pseudo-profound pseudo-political statement that "we're just like the Nazis" or any other similar message that some brainless Hollywood liberal might think to attach to a movie.
The sadism is what it is. It's Sadism Chic.