The first time I watched Monk, I fell in love with the series. Well, who wouldn't? As far as I recall, no detective has ever declined to give chase to a villain for fear of dirtying his shoes, or asking another detective to retreive some piece of evidence because he might get grease on his hands. And of course, it's just as amusing when his condition actually helps him to solve murders and catch crooks and stuff. However, after some time(about a few months) the novelty began to wear off. There wasn't anything new to keep me watching it. Soon, I stopped watching altogether. This may happen to you a lot later or earlier depending on how much you liked the show at first sight. Watching a detective cringe at such things like dust or dirt at the crime scene may seem...fun, at first, but soon there's just too much of Monk's obsessive-compulsiveness to actually get the detective part of the story underway. About 50% of the show is mostly Monk being...well, Monk. In my opinion, that's just too much. I would recommend this show to my friends, of course, and I know they'll love it, but soon they'll probably going to start switching channels-sooner or later.
Bottom line is that anybody who loves a good whodunnit would eat Monk up, but probably won't stick to it any longer than two seasons. Three on the outside.