Monk is equally likeable, but much more quirky and obsessive, which creates amusing problems throughout the show.  And there's always a "whodunit" mystery for him to solve -- sometimes it's clever, sometimes not, but you never mind too much, because Monk is just fun to watch, whether he's working or obsessing.

The supporting characters are good too, because they've avoided the old stereotypes, like the cranky police chief who's always on the verge of throwing the P.I. out of his office (the police chief in "Monk" actually respects Monk to a degree).  And Monk's assistant has only so much patience for Monk's idiosyncrasies.