For the curious, Neil Gaiman and Terry Pratchett selected the phrase "It was a nice day" to open their novel because it was the most "bland and innocuous" sentence they could create. And who would ever expect a story that hurtles toward the biblical end of times with every passing page to begin so simply?
In 2021, Gaiman told his Tumblr followers about the decision, saying, "The original opening of 'Good Omens' was 'It was a dark and stormy night.' And then we thought 'It wasn't a dark and stormy night' was a better take on it. So that was where the book started for a long time ... when we decided to begin it earlier, in Eden, we wanted another line that described the weather, and 'It was a nice day,' seemed like an excellent one. Bland and innocuous and a line that breaks every single rule about what you're meant to do with your first line. [Grab your reader by the lapels! Hook them in the throat! Never let them go!]"
So it isn't very surprising that Gaiman is rather proud of it and it isn't very surprising at all that he would choose to remind his television audience of the choice, either. To hammer home his pride, Jim states "That's more like it" after reading the first line of "Good Omens" out loud, as if it is the only way for any decent book to introduce itself. Subtle, Gaiman. Very subtle.