I could be wrong, but I think Gurren Lagann is also in the same boat.
In Japan it was just another once-ran daytime kids block anime (aired Saturday mornings at 9 AM or something like that) that happened to be by Gainax, but in America and Europe it was and is a cultural phenomenon! In it's THIRD airing on Syfy! Am I wrong or was it more popular in America than Japan?
While all that cannot be said about The Big O, it's a solid series that is like a bottomless pit of depth, and a 3rd season or at least an OVA/Movie would help to explain really what's going on! Gurren Lagann, on the other hand, begs for another arc with its ending but ended more conclusively than Big O by any stretch of the imagination. I think we're unlikely to see either, as Gainax and Sunrise have both moved on to other projects.
This Saturday Night, on [adult swim]: TOONAMI'S BACK, BlTCHES!! A New Bleach Episode (255) kicks us off at Midnight, followed by the SERIES PREMIERES of Deadman Wonderland at 12:30 and Casshern Sins at 1! Then, we've got 3 back-to-back classics: FMA:B Episode 32 "Fuhrer's Son" at 1:30, followed by GITS: 2nd Gig Episode 17 "Red Data" at 2 and Cowboy Bebop Episode 15 "My Funny Valentine" at 2:30! Also, watch lots of [as] ACTN shows including Durarara!!, The Big O, and more online any time you want at
http://video.adultswim.com/action/index.htmlElsewhere: New season of ThunderCats continues Saturday at 9:30 AM on CN! Avatar: The Legend of Korra continues Saturdays at 11 AM on Nickelodeon!