I've actually only ever played Diplomacy over Backstabbr.com with friends, so analogous to email/postal play (if you still count that as a board game). Completed several games now, and I've been wanting to do it in-person. That 1900 variant has more detailed notes than any other variant I've seen, and I'd like to give it a try!
Catan can be fun, especially the first few dozen times you play it. But it wears thin even for a casual group. We have better casual games these days. And even back then, we did: I found that eg Bohnanza released about the same time as Catan holds up much better to repeated plays; even though it looks much less impressive at first. The big problem with Catan is that the initial settlement placement determines so much of the rest of the game, and there aren't that many meaningful decisions left in the rest of the game.
I did most of my in-person games of Diplomacy when I was working in Cambridge, Cambridgeshire. I was working for a startup spun off from the local university, and noticed that the university societies were actually (mostly) open to the general public. So I just joined the Diplomacy society.
After a grueling day playing Diplomacy, I usually had second thoughts. (But that wouldn't keep me from doing it again a few months later.) But I did learn that I prefer play-by-email after all. The games are higher quality, and you can actually finish them.
Stripped of its cultural significance, chess isn't that great either for a general audience. It suffers from analysis paralysis. I would only recommend it to a niche audience.
I love Diplomacy; I played many games over email, in person and even participated in the German Diplomacy championship (face-to-face) back in the 2000s. Yet, it's also a very niche game, and I can see why some people would rate it low. I actually prefer the game over email, because it gives you more time to think, sending emails resembles the telegraphs of the early 20th century and I am less likely to burn out from a months long game with one move every few days than one very intense day of face-to-face play.
Btw, if you like Diplomacy, I recommend playing on the 1900 map variant. It's basically an improved version of the standard map.
See http://uk.diplom.org/pouch/Online/variants/1900-GG.pdf
Or for further reading https://diplomacygames.com/baron-von-powell-creator-of-1900/ or http://uk.diplom.org/pouch/Zine/F2007M/Roburn/1900.htm