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4-5: 3D and FMV explosion, it was something to behold.
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2-3: Super Mario Bros. changed the landscape of videogaming. Still, 3rd gen's early years were still dominated by arcade games in the style of 2nd gen. Consoles like the SG-1000 also overlap generations.
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1-2: Underrated answer. 2nd gen standardized actual game libraries, greatly expanded on genres when the 1st gen only had like 3 of them in very raw formats (sports which were Pong variations, light gun, racing), level progression even if most loops were short, in-game backgrounds, high scores. You have the progression of dots and sticks to Coleco and SG-1000 graphics that look like early 3rd gen.
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3-4: Back then when bits actually mattered.
Last finished: Activision Anthology (PS2) (Patches+Unlockables): Dragster, Fishing Derby, Skiing, Freeway, Ice Hockey, Kaboom!, Laser Blast, Tennis, Atlantis.