So Damn Happy compiles mostly nineties-era Wainwright songs, particularly from Grown Man, and new songs.
Regarding So Damn Happy's lighter tone, in comparison to previous release, Last Man on Earth, Loudon states that:
[One of the reasons I made this record is because] Last Man on Earth had a kind of serious tone to it, let's say. But this record, one of the reasons that we wanted to call it So Damn Happy - aside from the fact that there's a tune on the album with that title - was that we wanted to herald that it's lighter in tone. And there are some serious songs in it [but] there's some completely silly stuff, too, which I certainly hopefully never will forgo entirely. [...] It's a good time, and a lighter time, and I'm doing fine.