Reviews of Season 1, Season 2, Season 3.
By this final season, the show seems to have moved on to nothing but spectacle-for-spectacle's sake. And an obsession with penises, the most unpleasant of which is Cassidy (Joseph Gilgun) being tortured by having his foreskin removed hundreds of times (it regenerates - he's a vampire). Hitler and Jesus duke it out at the boardroom table, and God is shown to be powerful, petty, and capricious (in person: the previous three seasons had been exploring these possibilities in a more theoretical capacity). Blood, guts, and the grotesque dominate.
SPOILER ALERT: If you haven't but intend to watch this series, STOP READING.
In the end, Jesse Custer (Dominic Cooper) gets his discussion with God (although he had to die, go to hell, and return to get there). Whether or not you find it satisfying is a matter of personal taste: Jesse points out many of the things that atheists and agnostics have been pointing out for decades, which all boils down to God's neglect of his subjects and the suffering this creates.
To me the most irritating thing was the sloppiness of the ending. This is biblical in scale: I felt like it should have a clean ending, like a biblical story. But instead it's spectacularly messy. Jesse manages to thrash God in a fight after releasing Genesis, which makes no sense. The Saint of Killers killed God (good), but ends up on God's throne having declared his choice of hate over love (that certainly seems bad). The writers did manage one lovely twist: the angel and demon who love each other and have been fighting and fucking all through the second half of the season turn out to be the parents of Genesis and turn up to fight for Genesis and Jesse in the end (good). But their deaths turned out to be completely pointless as they fail to stop the Saint of Killers ... and then Jesse talks the Saint of Killers into not killing him (sloppy plotting). At the end of the series, Herr Starr walks away clean: I assume the writers thought this was funny and/or cool, but he was such a reprehensible character that I found it hard to swallow.
A disappointing ending to a series that, I suppose, was bound to end in disappointment.