He lives off the royalties of a song his dad wrote so he never meaningfully earned any income and sees human relationships in curiously absent ways. He has some interest in dating and makes the admittedly foolish mistake of thinking single mothers are low-effort and high-reward. His plan to meet single mothers backfires when his first date results in a hanger-on and her son who get the whole gang in trouble on an outing to the park. Although his dating scheme is foiled, he ends up forming an unconventional but meaningful friendship with the 11-year-old kid and that's how we have our titular story.
The American TV adaptation's pilot features most of the movie and book's plot in the opening episode which is somewhat of a necessity and not much of a concern because there's a lot more fun to be had. David Walton plays the lead and it's disappointing that he doesn't present us with a character significantly different from his California sun-dried womanizer in "Bent." Hugh Grant is by no means a great actor but he bought a sort of aimless whimsical charm to the role. In the film (and book) his lies to the eventual love interestish character about his child were fairly minimal and he makes an honest effort top backtrack on his lies. Walton is unapologetic and, frankly, quite sleazy. There's no middle ground in terms of whether to root for or against him.
The degree to which
the character (ok I'm just going to look it up) Will contributes to society is also changed here. Instead of the son of a song writer who sits around collecting royalties, Will at some point did something to earn money himself. He's a musician who's suffering from the dismantlement of his band but wrote a hit song once and lives on the royalties. The con about this is that as an ex-musician Will is considerably more cliched whereas Hugh Grant's Will was truly a unique creation. On the other hand, this scenario provides something more for Will to strive for in terms of his maturation: Reclaiming his friends and former band mates in addition to the regular sitcomey stuff (dating, career, etc.).
One clear strength of the TV show is the relationship between Fiona and Will which was relatively unexplored in the film. Toni Collette is a highly underrated gem who always brings something to whatever film she's in but she was underused in the 2002 film. Minnie Driver, one of those actresses who was famous some time ago but you can't remember if they're even still alive, has the potential for a great career reinvention here with a solid character role on TV.
As for Dakota, the object of Will's desire in the first episode, she was only intended as a plot device to get Will and Markus together but it might be interested to see her pop up again. I certainly wouldn't wish to see a romantic relationship blossom between the two but I'd want to see her pop up at some inopportune moment and make his life miserable.
It's hard to say if it's going to be a good show, but the source material is good enough that it's worth sticking around.
*I'm really not a book reader. I just like Nick Hornby novels