My opinion? He is funny - if you have a very dry sense of humor. This is not your everyday sort of comedy. It's not Blue Collar comedy. It's not slapstick work, either. You need a sense for satire to read Sedaris. So while I enjoyed it, I'm not sure I'd recommend him to everyone I know.
The most accessible of the six stories is the first, "SantaLand Diaries". It details the author's brief stint as an elf in Santa Land at a mall. This was probably my favorite piece, most likely because I've worked retail at Christmas. No, not as an elf, although my lack of stature would probably make me a shoo-in for the gig. Sedaris paints a picture that is pretty much the modern version of the Santa scene in "A Christmas Story" - if the scene was told from Old St. Nick's point of view.
The other pieces aren't less humorous, just not quite as overtly funny. And again, you have to be able to discern the hint of satire and such; some may read the other pieces and believe them to be autobiographical works as well, which they clearly are not. My other favorite in the book is "Front Row Center with Thaddeus Bristol", a hilarious look at Christmas pageants from a "reviewer" of such shows.
If you like very intelligent, dry humor, I'd definitely suggest David Sedaris. If you prefer more overt comedy, try someone else.