6. S.T.A.L.K.E.R.: Shadow of Chernobyl
Development begun: 2001
S.T.A.L.K.E.R. was originally slated for a 2003 release, though it missed this mark by a long shot. It suffered a few embarrassments during its lengthy development, including an unstable alpha build leaking in 2003 and a buggy release in 2007.
It even made Wired Magazine's 2006 Hall of Vaporware, along with Spore and, naturally… another game that may or may not appear on this list (you can probably guess which one).
In spite of its issues, the game was met with positive reception, and its post-apocalyptic setting dripped with gooey atmosphere. THQ went on to publish Metro 2033, an incredibly underrated game that shares the apocalypse theme with S.T.A.L.K.E.R. and owes a lot to its eventual success.