Monk was never much more than a perfectly pleasant show, but, in the end, that was probably enough for its millions of fans. When it first came on the air in 2002, as Alan Sepinwall has pointed out, the series was basically doing something the networks had given up on. As the networks rushed to meet cable halfway in terms of edgy material, ABC passed on Monk, simply because it didn't seem to fit any network model at the time, and it slipped to USA, which took a substantial chance on the bet that people still wanted to watch the sorts of light dramas that had been so popular in the '70s and '80s and that they would find a light drama in their cable package. The network was right, and Monk ended up becoming one of the most significant shows in television history, even though for much of its run it was nothing more than pleasantly innocuous.
Yes, I said one of the most significant shows in TV history. As Sepinwall points out (and as Jaime Weinman elaborates here), Monk proved that basic cable could have ratings successes by rushing in where networks feared to tread. Since then, nearly every basic cable channel has found a way to chase a niche audience by figuring out some genre that the networks weren't exploiting and exploiting the hell out of it. Family sitcoms have moved to The Disney Channel, Nickelodeon and ABC Family, while less gory crime procedurals are now at home on TNT. Many other channels are indulging in reality, sure, but it's often a kind of reality the networks have either abandoned or never indulged in in the first place. While there are fewer content standards on cable, cable channels are often more likely to take fewer risks and just present something enjoyable.
And a lot of that is directly attributable to the fact that when Monk debuted, it was a pretty big hit. While the show never had the strongest of mysteries, it was, at least for the first few seasons, terrifically funny, bolstered by a very strong performance from Tony Shalhoub, who was always a little underrated as an actor before Monk and now can pretty much do whatever he wants. Not everything always worked on Monk – in particular, the show's one tip of the hat to serialization in the Trudy mystery never really hung together – but the stuff that did work, namely Shalhoub's performance, the very funny writing from a team led by Andy Breckman and Shalhoub's chemistry with Bitty Schram and later Traylor Howard, was good enough that the show was the perfect end of week treat. It also helped that the show was on during the summer, a time when TV was still pretty sleepy back when it began.
Since Monk's debut, the entirety of the USA network lineup has been gobbled up by Monk-alikes. Monk wasn't the first scripted show USA put on the air, but it was the one the network aggressively copied the tone of going forward. Now, practically every show on USA is a throwback to an older genre of shows and nearly every show on the network is a lighthearted comic romp through whatever genre it's a part of. Whether it's Psych, White Collar, Burn Notice, Royal Pains or any other show on the network, Monk has ended up defining the channel, for better or worse. Sometimes, these shows can feel a little shoddy or overwritten, but the best of them are enjoyable TV pleasures that don't aspire to much more than giving viewers a good time. And there's nothing wrong with that. Monk, after all, did it very well.