Finally learned this last week, after a while of having wanted to. For those who don't know, it's a Feld game. For those who don't know what a Feld game is; play Trajan, Macao, Bora Bora, or Castles of Burgundy. All designed by Stefan Feld, all great, all with a similar feel. Anyway, Castles is the simplest of his games that I've learned... you can teach/learn it in about 5-10 minutes, as opposed to much longer for the others. But the strategy is just as deep.
I've now played twice, and had a lot of fun both times. Both 4 player games; the second time I managed to win on a tie breaker. Which is amazing that you would have a tie in a game where we scored 232 points! Oh yeah, and the English rules for the tie breaker are mistranslated and the opposite of what they should be; luckily I'd been browsing the BGG forums on it recently, otherwise we would have just looked at the instructions and seen that I'd lost, not won.
Anyway, it's a combination of set collection with a little worker placement mechanics. I'm terrible at writing actual reviews, but check it out, it's great.