Maybe this only applies looking at it from today's point of view, but Metroid on the NES was complete garbage, then Super Metroid was a masterpiece. Probably a lot of examples if we do that NES > SNES transitions, anyway.
On an example most people would be able to agree on, though, as much as I've moved on from this series since my teenage days, the evolution of GTA from the PS1 games to the PS2 was remarkable.
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