The best game of the three is Fortune's Tower, a Blackjack-like card game where you place a bet and either "hit" for another row of cards hoping to increase your bet multiplier, or "stay" and take what's on the table. Of course, you go bust when the cards fall a certain way losing your bet, or you can get a jackpot if you hang in there and get every card in the deck on the table without going bust. The game is about as much fun as playing computer Blackjack, which could be a good or bad thing depending on your outlook of that game.
Keystone is the next best game. it is a cross between Roulette and Craps where you place bets on the table for numbers, colors, and other winning possibilities, then roll three dice to determine what wins. Of the three games, this is the most difficult to learn and master as there are ways to bet more than you can possibly win, just like real Roulette or Craps.
The worst game by far is Spinnerbox, which is a Fable version of a slot machine. Choose your box, set your bet, and press the A button. Over and over again. You might has well program a robot to do this for you, because it is boring as all get out. There is really no interaction here, and you very quickly grow bored watching the dials spin and click to a stop. While Fortune's Tower can be a lot of fun for a reinvention of Blackjack, and Keystone is a well designed table game, Spinnerbox seems to be just tacked on for the sake of having three games.
If you are persistent, you can fairly easily rack up all 200 gamerpoints in the Pub Games. You can also gain a pile of prizes that range from useful (skill boosts) to ho-hum that you can transfer to your Fable 2 hero. And unless you use the (now patched) cheat, don't expect to make a fortune. In fact, it is more likely that you will be in debt. If you decide to merge your Fable 2 hero with your Pub Games character, you will transfer that dept as well as gaining the items you won in tournaments. Good thing money in Fable 2 is easy to come by.