I had the first Fable, and like many of my gaming fellows I was disappointed with the experiencce. It was far too short and not nearly as engaging as a half-decent RPG should be. I had no motivation to advance.
Peter Molyneux really talked up the first game, which blew up in his face. When he started doing the same for the sequel I reacted with disdain. Why should I be listening to him now? His answer: a dog.
Fable 2 is much like Fable 1, but a few small differences has made it a little more palatable. The story and characters are more engaging now and to some degree that makes you want to progress. Production values have improved in accordance to the current generation's standards, and the dumbness of the first game's mechanics have gotten a little better balanced, though not any deeper.
The dog acts as an interesting companion and can help you in treasure-hunting, missions and combat, but definitely does not induce the kind of heart-swelling that Peter hoped it would. I find it cute when you run and it scampers to keep up though...
The voice of Zoe Wanamaker as Theresa was pretty good, and the rest was decent, though if you can't stand heavy English accents, you will be put off.
All that said, it's a glitchy release, with slowdowns and malfunctioning events almost common (though a patch is supposedly in its final phases).
The combat is extremely simple and not very intuitive. You have 3 paths to combat, Strength (melee, also controls HP), Skill (ranged, controls speed and evasion), and Will (magic, boring because there are far too many spells that do exactly the same thing). Any decent RPGer could figure out how to min-max a character in 5 minutes of reviewing the numbers and getting into a few fights. There's very little in the way of weaknesses and resistences, and what you wear has no armour effect.
There are things like renown (how popular you are), purity (good or evil) and fatness, but while they're all core elements they don't seem to demand your attention at all. Social aspects are front-and-centre, and you can marry, have sex, build a family, own property and busniesses, which is all fine. What I didn't like is how everyone seemed to be bisexual, even when their profiles said otherwise. Trying to seduce the girl in front of me usually had some random male NPC behind me becoming enamored at the same time. Annoying.
Unlike the first game, the style the game world takes this time is very much like the European pioneer eras, complete with flintlocks being the ranged weapon of choice. My problem was that (IMHO) fashion and items were really ugly back then. I would have either stayed fantasy or gone steampunk.
The game is still brutally short, and you can probably completely wreck this game in under 40 hours, which is pathetic for an RPG.
All-in-all it's not a game I'd recommend unless you're a VERY casual gamer, and taking that into account such a gamer would be better off playing something else. RPG-wise, try the .hack//G.U. series.
Unless Fable 3 makes some serious changes, I won't even give it a look.