Storytelling in games is different from any other medium. Unless you've made a visual novel, where you just allow a player to click through a story created by a writer, then you're going to have to factor in player decision.
Speaking with GameSpot (via PC Gamer), Larian Studios' Swen Vincke spoke about how much effort goes into creating a good video game story. "Narrative design, dialogue writing, making sure that you have all permutations covered, arcs over longer periods of time across multiple games, these are all different disciplines and they require specialization and so you need people that are used to doing these things," he said.
Specifically, Larian has quite a unique approach in how much it allows for the player to mess around with its stories. "We are a company that iterates a lot and needs a lot of story because when you play our games and you decide to do something, you want your story to continue. So, somebody needs to have thought of this."
Larian currently has two projects being worked on, and to help build up the narratives for these games, Vincke says that it is building a storytelling team to help with the writers build up future worlds and narratives.