Today, I learned that there is not in fact a well-regarded songwriting pair from the seventies named Gilbert and Sullivan. It's just that every time I ever heard the name Gilbert O'Sullivan, I'd thought I was hearing two last names, like Rodgers and Hammerstein. Yeah, I'm an idiot.
Probably the first time I encountered the song Alone Again (Naturally) was on Jonathan Coulton's soft rock album Some Guys. It didn't blow me away immediately, but I later heard the song covered by YouTuber Sammy Copley. (video link) and found myself really digging the chord changes. The song's composition is awesome, and I've now gone back and listened to Jonathan Coulton's version many times, as well as digging up at least a couple other versions.
This may be the first time I've been a fan of a song not specifically for the performance, but rather for the songwriting. You kick ass, mister O'Sullivan.
EDIT: It's now later in the day, and I've been listening to some Gilbert O'Sullivan music while I work. While I've found some I really like, (No Way is excellent) I really don't know about some of this. In the song that's currently playing, he sings about how he slapped Mary in the face during an argument and that he's sorry. WTF? Not cool. Another song is actually entitled "A Woman's Place", and it's not ironic. He sings about how a woman's place is in the home. Man - I still like that one song, but I'm having some trouble with the misogyny.
EDIT: Apparently there is a Gilbert and Sullivan who worked as 19th-century playwrights and wrote comic operas such as The Pirates of Penzance. I may have heard their names at some point, which would only have added to confusion.