The survey seems to have focused on games I didn't play, even in series that I did play. For instance, played FO1-3, but not NV. Played BG1, not 2.
I also played TES 3: Morrowind VERY extensively (probably 5K-10K hours over more than a decade), TES 2 briefly (frustrating, since the mouse doesn't behave properly through the DOS emulator on my current system), and TES 4 for a relatively short time (50-100 hours) before deciding that it lacked almost everything I liked about 3's open world and unique culture, as well as converting from an "all or nothing" to a "can't fail" task system (neither of which is realistic, but I'll take a simplistic approach to failure over none). To date, Morrowind is clearly my favorite and most played RPG, especially with mods (I spent a couple of months roving up and down practically every nook can cranny of the first Tamriel Rebuilt landmass section, looking for placement errors and other bugs), and ranks among my top 5 games overall (along with HOI3).
Mount & Blade is another favorite, where you have elements of an open-world RPG, a FPS skirmish combat system, and some aspects of a rudimentary empire builder which were expanded upon in mods. There are multiple ways of playing (a big positive), and no overarching storyline at all (which is both a good and a bad thing). There are several good complete overhaul mods for it, which essentially give you a completely new game on the old engine.
The X3:TC space game has strong RP elements, and a heap of replayability with different characters and approaches to playing, but character interactions with the NPCs are extremely limited. The sequel, X: Rebirth, completely missed the mark about why players liked X3.
Achievements? Why? Who am I trying to impress?