I haven't seen the film, and I quite possibly won't. But this paragraph from Last's review is great, especially the last line:
Stripped down to its elements, Closer is the stuff of European bedroom farce--dozens, if not hundreds of French and Italian films have used the same basic engine. The difference is that the material in Closer isn't played for laughs. It is instead mined for psychological and epistemological truths. Earnest truths about innocence and need and fidelity and honesty. Not since American Beauty has a film wanted to dive so deep into so shallow a pool.