Quentin Tarantino has always had lots of fun writing playful dialogue for bad guys, sadists even. The criminal who tortures the cop in Reservoir Dogs had some charm, to say nothing of a sense of humor and a familiarity with pop culture. Those mobsters in Pulp Fiction who love to talk about the ins and outs of European fast food make their living killing people. Tarantino's never been especially interested in pursuing the morality of his characters or the morality of his own representations of criminal life.
The minutiae of everyday life (long conversation about tipping practices, anyone?). The way a fetish-like obsession (for Tarantino, an obsession with movies) creates an alternative universe. Those things interest him a great deal.
Inglourious Basterds--which let me say I absolutely, positively loved--has mostly gotten very positive reviews for its ambitious scope, playful approach to narrative, and most of all the performance of the actor playing Nazi Colonel Hans Landa. A few reviews, notably the N.Y.Times, New Yorker, and the Orlando Sentinel have pointed out not only the film's violence but also called into question the ethics of representation involved in parallel stories (obviously fiction) about a band of violent American Jews who hunt Nazis in occupied France, as well as the aforementioned Nazi Colonel who--like many Tarantino baddies--has urbane charm.
First, the Landa character. How many sadistic bad guys in fiction and film have been represented as cunning and charming? Of course a *Nazi* bad guy is worlds apart from a "purely fictional" bad guy a la Hannibal Lecter. The ethical dynamics shift when the characters have roots in history, especially THAT moment in history. But in my view Landa is never defined by his charm at the exclusion of brutality. No, this is not a film interested in moralizing (and that in and of itself might be a problem for some viewers), but neither is it a film that fails to balance the urbane with the vicious. That balance creates the film's suspense, in fact.
Second, the band of "basterds." They combine the expected and the unexpected. As viewers, I think we expect the genre tropes they represent: the war movie (the basterds have both a 'gee whiz,' all-American, baseball fan G.I. thing as well as a cigar-chewing, Dirty Dozen thing going on) and the gore movie (not for nothing does Eli Roth of Hostel fame play one of the basterds). We don't necessarily expect the global historical revisions or the over-the-top spectacles the basterds help to orchestrate. In other words, they defy simply categorization. And that helps the representation go beyond something merely pornographic (as in, one intended outcome only) or exploitative (though a bit of the latter is part of what Tarantino mashes up to create his unique vision). As the AV-Club points out, Inglourious Basterds is among other things an antidote to sterile middlebrow representations that teach us that Nazis are bad.