Crowning Moment of Awesome: Even if you don't want to read the rest of the series, and you might not, it's worth tracking down issue #3 of the original series to see Wormwood's guided tour of heaven and hell.
Babs flipping off Nigel the Beast with Seven Heads and telling him "fuck off"
Crosses the Line Twice: Pope Jacko and his penchant for coke-fueled orgies with scantily-clad nuns, Wormwood swapping a dude's nose with his dick, God as a constantly masturbating, levitating moron, killer eunuchs, every single TV show Wormwood's responsible for... look, it's Garth Ennis.
Fridge Logic: Wait... Wormwood can't cure Jay's perfectly mundane retardation by getting HIT ON THE HEAD!
Fridge Brilliance: In the final issue of the first series, Jay is cured by other means - and begs to be killed. In a cured state, he remembers all the things he went through, and how little it amounted to in the end. The only way he can stand to live is as a retard.
Wormwood: Jay's suffered for the human race twice now. He's done his bit. And me... Well, as I never ger tired of saying, I am the Antichrist. So it looks like you'll have to sort out your own problems, folks. Because me and my pal Jesus? We're not about to do shit.
Of course, Jay starts to recover naturally near the end of the second series and decides he does want to continue helping people.
Nightmare Fuel: The visions of Hell that are shown to Paul Carnovitz in The Last Battle #1, particularly if you're a parent of young children.