I'd say, worth my 20 bucks.

User Rating: 9.1 | Fable: The Lost Chapters (Platinum Hits) XBOX
When I played the original Fable I was completely and utterly baffled. I never thought it could be made better (well other than making it longer). I thought, after playing through the original game again on my 360, I'll just buy it. The gameplay would be perfect, except for the longer loading times and the sometimes laggy cut-scenes. Of course I got my 360 because my Xbox broke, so I have no way to compare how it runs on both. The graphics are good, except for when you are making your way into highly detailed areas. Some objects, such as trees and stones, don't load quickly enough. Also, alot of the character designs are pretty ugly and choppy looking.

I agree with the Gamespot Reviewer that this game is too short. I played every single side quest, got all legendary weapons, opened all demon doors, along with the main storyline, and it only took around 14 hours. Sure they improved the length from the original, but like GR said the extra content really feels like it was stacked on the end.

If you haven't played the original Fable, this is a must have.
If you have the original Fable, but you haven't played this game, put that "extra" 20 bucks to good use.