What system was the biggest improvement over its predecessor (in overall quality, not graphics) and why?

[Zkuq]

I have enough experience with PlayStation consoles only, so I'll say PS2 to PS3. PS3 enabled open world games in a way unlike before, and janky gameplay (e.g. because of poor cameras/controls) largely became a thing of the past. Online play was also enabled for the masses (at no extra cost, I might also add). Some might also appreciate the wireless controller and Blu-ray movies. I'd also mention motion controls, but I don't think they were utilized very well in most cases. Oh, and digital distribution is probably something many appreciate as well! There's downsides as well, like limited backwards compatibility, but I think the net improvement is still quite good.