Tech-wise Gamebryo was revolutionary and its successor is still unmatched in its particular niche. It's not the graphics or the mechanics or the writing, it's the engine. No matter how much shit Bethesda gets, there's a reason you haven't seen a Skyrim But Better by now, and it's because we're still barely getting Oblivion But Worse.

When people were trying to create a randomizer to the original version of Dark Souls 2, they found it almost impossible because you literally could not place certain NPCs or enemies in certain areas because everything in an area came packaged together. You might need an AI package from one asset list, but you have to load the whole asset list, and there's no memory for that. Or if there is, one entity might have code attached to it that conflicts with another and you've just caused the renderer to bomb out. Lots of games are like this, even now, and the ones that aren't will cook hardware 5x more powerful than the 360 was for half the complexity.

Meanwhile in any Gamebyro or Creation game, you can drop anything in the game, anywhere in the game. You can give it one line of script that tells it to cross the entire world and it'll do it, even if it has to pass through ten separate loading zones and three worldspaces to do it, and you can personally intercept it anywhere along the way. And you might know of a game you think did something like that once or twice, but I guarantee you nine times out of ten, it was a trick, not something the engine can just do.