Had to think about this one for a while...
The ones that immediately spring to mind:
- Fallout 1
- The Age Of Decadence
- Alpha Protocol
- Legend of Grimrock 1 (2 is quite a bit longer)
- Serpent in the Staglands (25 hours might be cutting it close, but I don't think it's that much longer either)
- System Shock
- Knights of the Chalice? (Somebody fact check me on this, I seem to recall it wasn't the longest game but I'm not sure)
- The Bard's Tale Trilogy (I recently finished the first game in about 25 hours, this remaster cuts down on the grind a little it seems)
- Vampire: The Masquerade - Bloodlines
- Expeditions: Conquistador (more along the lines of 30 hours)
- The Witcher 2 is actually not very long either
If you're willing to venture outside of the realms of Official Codex Approval:
- Driftmoon (more of a charming adventure with light RPG elements, but you might still enjoy it)
- Freedom Force (also not really an RPG and more of a real time tactics game, but I like this one nonetheless)
- inkle's Sorcery! games are actually CYOA games with some RPG elements (AoD anyone?), but you also might enjoy them and they're pretty bite-sized
- All three Banner Saga games
- Hard West (again not an RPG but I do believe some people on the Codex, including me, do like it)
- Both South Park RPGs
EDIT: Started writing this down before the post by
David Cernat, sorry for the duplicates