In bookverse, Faramir is a gentle-hearted man who, while renowned as a warrior, is also known for his wisdom. He offers help to Frodo and Sam almost unconditionally upon learning of their quest, and even dispenses mercy to Gollum. He turns down the opportunity to claim the One Ring, claiming that he would not take it 'even if [he] found it by the wayside.'
Canonically, Faramir falls in love with Éowyn while they are both recovering from their encounters with Nazgûl in the Houses of Healing. After the war, the two wed and are given the land of Ithilien by King Elessar.
Here, Faramir is made into rather a jerk at first. Instead of politely questioning the Hobbits, he immediately has them captured for interrogation. He also has Gollum beaten up, threatens to take the Ring from Frodo, and hauls all three prisoners to Osgiliath to send them to Denethor. After the Nazgûl attack the city, however, Faramir reverts to his book-verse persona and lets them go. (According to Peter Jackson, Faramir was made into a jerk at first so that he could have character development.)
In Faramir's defence, however, Frodo's character is so warped by this point that Faramir can almost be excused for his reaction. When Faramir first finds him and Sam, the first thing Frodo does is evade his questions about what they're doing in Ithilien, and outright lies to him about traveling with Gollum. Therefore, it isn't really surprising that Faramir treats them with more suspicion than he does in the books.
Either way, though, it's an unsatisfying moment for book fans.
In Badfic Edit
Faramir has an unfortunate tendency to be the subject of evil!Denethor's abuse. While it is true that Denethor displays clear favoritism for Boromir, there is no case at all for outright abuse, but this doesn't stop the badficcers. Depending on the fic, this abuse can result in a hurt/comfort relationship with either Boromir or a Mary Sue.