There are already some huge maps out there, Just Cause 2 and 3 both have maps at around 1000km2, and those games are beloved by their players. But if the next Cyberpunk game was announced with Night City now being the size of an actual large metropolis, say like New York, would you say that’s too big? What determines what “too big” is?
Depends on a lot of factors like what the actual game is.
A sandbox game, bigger is better. Like Minecraft. If the goal is exploration and resource gathering you can plop me into an infinitely generated map and I will be happy.
Outside of that, narrative games can be too big if there’s nothing to do in between points of interests. I don’t mean like side-quests, but more like random encounters or crafting/gathering stuff. There has to be something there I can either get distracted with or to “on the way” to the next location.
I think a lot of games want their cake and eat it too. It’s not an open world game, but Final Fantasy XIV promoted the Heavensward expansion with the zones being like 5 times bigger than the base game…
…but there were only 6 of them and between already being able to teleport to each zone there wasn’t any difficulty navigating the zones and they added flying which made them seem smaller than the base zones.
1.0 XIV had impressively sized zones that were unfortunately very copy pasted and between the rushed release and the engine limitations enemies were very spread out.
Again, depends on the game.