I won't pretend it is an ultimate list, since there are far more RPG that i want to try than RPGs i already tried.
I would say that one of the things that stuck me into Fallout 2 was the level of content you would find into the city. I usually spend 90% of my playing time INSIDE the cities, talking with npcs, thant in filler dungeons full on generic stuff to kill. It might not be important for everyone, but it means a lot to me to just be able to spend my time exploring the lore, the personality of the npcs, socialize with them, etc... It is a billion times better that just killing random stuff. There are already enough games for killing stuff. Anyway, the level of city content compared of filler content is far higher in Fo1-Fo2 than any other episode of the franchise. Amongs those Fo1-Fo2 cities, those that stuck the most for me were New Reno, Broken Hills, Vault City, The Hub & Necropolis. I also loved the Strip/Freeside/Vegas neigborought in FoNV, as it not only fit very well with the lore, was interesting, and provided me HOURS of contents while not leaving it, not being forced to meet random filler monsters. Unfortunatelly, it was the only place like that in the whole FoT-FoBos-Fo3-FoNV set of episodes that provided me so much.
On other RPG that i played, i fell really in Love with The Witcher 1's Vizima. I had the opportunity to play two whole chapters, tons of hours worthy of contents inside that big city, full of believable and living npcs. It reminded me the pleasure i had in exploring Fo1-Fo2 cities, meeting those people, interacting with that world, investigating, discovering the lore, see how it evolved. I mostly enjoyed Vizima, and much less the countryside, but they did that city totally right IMO.
Other than that, i think there are more RPGs to try out there to have a better list.