Cancelled or bowed out--doesn't really matter to me--BSG had a stellar first season-tightly written, epic storytelling, heavily serialized, urgency of purpose. Then the last 2.5 seasons it was all over the map. It really could have cut out a lot of crap and merged seasons 3, 4 and 4.5--trimming a season and a half out.I always got the impression (my own opinion mind you) that Moore and company decided to end their show at Season 4 to avoid cancellation. BSG's ratings were probably at their lowest point before Moore's decision. It was a prestige show for Sci-Fi so they likely didn't want to cancel it but at the same time the ratings were so low, they might have had to eventually. Deciding to end the show at Season 4 allowed both sides to save face.
I mean we had the tedious love quadrangle, the Baltar cult that just dragged on, the stupid Six/Tighe/Ellen triangle, the stupid Six baby plot, a whole bunch of uninteresting filler, the mythology just fell flat at the end. The only thing that salvaged it was a stellar series finale in "Daybreak".