The Talos Principle started as Serious Sam 4

Croatian developer Croteam is mostly known for the Serious Sam series of run-and-gun blast-the-shit-out-of-aliens shooters, which is why its puzzler The Talos Principle was such a surprise.

was such a surprise. It’s more Portal than Duke Nukem, filled to bursting with puzzles and a challenging philosophical narrative. Again, surprising from the team that made Serious Sam—especially because The Talos Principle actually began life as Serious Sam 4.

In a GDC post-mortem for The Talos Principle titled “Reactive Game Development,” Croteam talked about how The Talos Principle spun out of development on the next Serious Sam game. While working on the “jammer” mechanic that eventually found its way into The Talos Principle, the Serious Sam team kept brainstorming new mechanics that seemed like a better fit for a new project. So they decided to start work on a completely new game.

Croteam’s Alen Ladavac and Davor Hunski stressed how important they think it is to be reactive in game development, because there will always be unforeseen problems or situations or opportunities during development. They said that that’s especially true when developing a wholly new game, rather than a sequel: you can’t know what you want until you see it.

Croteam’s focus on reactive design informed The Talos Principle throughout the entire development process, starting with internal testing. The team members individually built puzzles, then extensively tested each other’s puzzles and rated them for fun and difficulty. Getting stuck on puzzles in testing led them to The Talos Principle’s nonlinear structure, so that players always have multiple puzzles to tackle. External testing led them to more refinements, as the team cut out redundant puzzles and shortened the game’s Rome segment based on that feedback. They also used automated testing, running a bot through the puzzles, which they say came out to 15,000 human hours of testing.

Not everything went well—Croteam acknowledged several mistakes, such as misjudging the time required for localization—but the key lesson was that getting and reacting to feedback quickly is vital. Had that iterative process not kicked off during the development of Serious Sam 4, The Talos Principle would never have been made.