The only thing these games have in common is the artwork, theme, publisher and role selection mechanic. Alhough with similar themes (building your infrastructure and producing and selling goods), most of the game mechanics are completely different. Basically:
- Puerto Rico is a boardgame with lots of bits, more rules, takes longer to play (~90 min). Basically a good representative of Alea game series intended more for the gamers and people appreciating a deeper game.
- San Juan is a somewhat light cardgame. It takes less time to play (~45min) and is very similar to a "dumbed down" Race for the Galaxy, but much easier to teach to new people, so it is a good game not only for gamers but also for non-gamers and casual gamers.
So answers to your questions:
- Game play is completely different
- It is significantly easier to teach new people
- It is definitely worth buying even if you have Puerto Rico. (It will be a nice travel size game, which takes less time). Keep in mind, if you have Race for the Galaxy, then I would say - no need to buy this also.
P.S. They are both really good games, just really different.
