Its a gambling game, with an extra bonus.
The graphics are good, nothing to complain about there.
The sound does its part, and the music does too, but you'll be focusing too much on the games to really enjoy it.
The first game, Fortune's Tower, is an original game, its fun, but at times it can be brutal, unlike the other two games, it does take some skill, but is mostly based out of luck. Probably the most fun out of all of the games.
The second game, Keystone, is pretty much in the middle. Its pretty roulette, but with a twist. Its pretty complicated, but you need a lot of luck to win at it.
The third game, spinner box, is the worst of the three games. Its requires absolutely NO skill, and ALL luck. Its really no fun to play because you end up losing all of your money most of the time.
Is it worth buying the pub games if your not going to get Fable 2?
No
Is it worth buying in general?
If your a fan of gambling, yes.
If you get frustrated easily, no.
If you want to earn free gold in the game by playing free tournaments, yes.
Should you pick it up as a free part of the pre-order?
Yes, Its free, what can you lose?