Well, for one thing, there was no FBI agent. The main character was a lead scientist at CERN, with the name of Lloyd Simcoe. That was one of the names the TV series kept. There was another scientist who tried to prevent his murder after realizing why he hadn't had a vision, and there was Lloyd's girlfriend. Those were more or less the main characters, and were all reactive to the situation and the world around them. The novel had more of a feel of internationalism rather than being focused in LA. A big chunk of the story had them wondering if the LHC experiment had caused the blackout.
But why would that make the characters more interesting?
The big problem with the show wasn't so much the logic of the plot, or the fact that most characters were American (perfectly normal for an American show), or that they weren't scientists (who can be just as boring as FBI agents and doctors), but the fact that they didn't make the audience care enough about their trials and tribulations to keep watching.
The most successful characters were Demitri and Janis, and that's because the actors were likable. Demitri's story was also good, being nice and straightforward: his life is in danger and he's trying to survive. Janis succeeded despite her plotline, which was cliched (the triple-agent mole being right outta
24). It was also hard to get behind the way she fussed about having exactly the same baby as her flash-forward - wouldn't she be able to love any baby she gave birth to? That struck me as weird and maybe creepy.
Marc Benford in particular annoyed people because he was too whiney and mopey. We want our main character to be more heroic than that, someone we can root for and respect. He can have troubles heaped on his head, but when we catch that deadly whiff of self-pity, we lose sympathy for the guy and change the channel.
But again - was that the writing or was that the actor? Was Marc actually written as mopey, or could Fiennes or another actor have made him a put-upon but stoic everyman who would have earned our sympathy and respect?
For the suicidal doc (even at this late date, I don't know everyone's names!), the problem was the plotline. Who cares if he hooks up with the Japanese girl? Sonya Walger did a good job in her role, but it was silly that she should be "afraid" of cheating on her husband, something that is entirely under her control. Without that, there's no dramatic tension for her character, except worrying about her drunk hubby, but that just makes her the worrying wife, bleah.
I never bought Dominic Monaghan as a bad guy. He always seemed to be too much of a casting stunt - "look, we took the hobbit/Charlie on
Lost and made him a bad guy, bet you never expected that!"
So it seems that the problem was a mix of poorly written character arcs and poorly cast roles.