Game development once you have the core technology in place is mostly iterative with content and play testing .. but requires a lot of waterfall foundational work - production design, sound , engine , core gameplay and graphical design ideas aren't really something that evolves from requirements discovered from a customer or PM that come at you gradually.

It's more like lean product development of a car or other product: you have design targets and may do concurrent engineering / spikes to explore the design space iteratively, but eventually you converge on what will be achievable (or you get stuck in game development hell), which point its a matter of bug fix triage and endless tweaks from game testing feedback. It's iterative but not what one would call "agile"