I never played Just Cause, yet I've got a whopping 50% logged into the second one; I never even heard of Red Dead Revolver, yet I finished Redemption; I only ever played GTAIV; I bought Rise of Legends before I brought Rise of Nations; I played Battlefield 2142 and Bad company before I played Battlefield 2; I only ever got the Modern warfare games from the CoD franchise; I had Fable 2 before I had Fable; I got Vegas 2 without having played any of the Rainbow 6 games, and likewise with GRAW 2; I played though C&C 3 and Kane's Wrath twice without having played any of the others; I got HALO 3 before I did any of the others; I finished God of War 2 & 3 before I finished 1; I got The Two Thrones and PoP 2008 without having played Sands of Time and Warrior Within; and I played Half-Life 2, Team Fortress 2, Fallout 3, and Jedi Outcast before playing their respective precursors.
Phew!