I think Ratchet and Clank were really close to their concept art, http://playstation.joystiq.com/photos/ratchet-and-clank-concept-art/373762/ to their 3D form. http://ps3.gamespy.com/dor/objects/819456/ratchet-and-clank-ps3/images/ratchet-clank-future-tools-of-destruction-20070409010524742.html
Although the upcoming game, Borderlands, is shaping up to look almost like concept art itself,nice!
http://news.bigdownload.com/2009/05/01/new-borderlands-screenshots-keep-showing-off-the-concept-art-st?icid=sphere_blogsmith_inpage_joystiqnintendo