Fable 2 started the downward slope. Killing off the Heroes Guild right away, bland story with only a handful of even half-memorable characters, cluttered menu system that's more confusing than it needs to be, having to be still to cast magic, no interesting quests, there's just so much wrong with it to me.
And this is just it by itself. Fable 1 you could honestly make a case for it being one of the best rpgs of that generation, up there with KOTOR, Baulder's Gate, and Morrowind. But Fable 2 and 3 against Oblivion, Skyrim, Fallout 3 and NV, Mass Effect, etc? They don't stand a chance, which is depressing as 1 set up such a great foundation.
I really don't compare the Fable series to other western RPGs because it's a RPG, Action Adventure and Sims all at once while also not truly being one of those things. That may seem bad, but its smorgasbord of genres is what makes it great (although I would always want more depth in all of its component genres). I liked Fable II more as a game than I did the Fallouts. Skyrim with mods is my favorite game of all time and while Fable can't match Mass Effect's character interaction and dialogue I didn't really expect it to.
Combat in the series has never been a strong point but I didn't mind the simplicity of Fable II, although not being able to move while flourishing and casting was annoying. Fable III somehow took Fable II's combat and made it worse. Remember how slow time was a potion instead of a spell (truly awful design choices)? Fable TLC edges out Fable II in terms of combat. I love the stylized two handed weapons that were too heavy to hold upright, more unique spells, etc. I can't say combat is why I played Fable, although I'll take Fable TLC and II over FO3 and NV's awful shooting (of course I'm not playing FOs for combat either).
On the character front I disagree completely. Jack of Blades has awesome character design and I like the lore with the void and the Court of Blades that was never fully explored. Apart from JoB, your mother and Theresa I found the supporting heroes to be rather annoying which was purposeful, but they don't hold a candle to Fable II's supporting cast. Theresa was all the more interesting in Fable II and Zoe Wanamaker gave a great performance. Then you have Reaver who beats out anyone in Fable TLC and Hammer who didn't fit the mold of most female characters in RPGs. Lucien was also a lot better than your average RPG villain as he wasn't some ancient evil, just a corrupt and rich leader with a fascination to bring his family back. Side note, Fable III had the series' best cast, Ben Kingsley, Zoe Wanamaker, Stephen Fry, John Cleese, Michael Fassbender, Simon Pegg and Naomie Harris.
On quest design, I think Fable TLC is better than II, but it's close and II has some great quests (Chesty, pirate ghosts, Normanomicon, raising Lady Grey). While design is better in TLC in terms of objectives I like the context of the quests better in II as well as the atmosphere. Wraithmarsh and its environmental story telling is great.
I don't think PG will have such an easy time with Fable as many expect. There's a lot they could miss and get wrong about Fable. I would expect better combat, but I'm also worried it will be a by the numbers open world and lack the charm of the originals.