We went to U Modre Kachnicky and it was really really good. We had reservations at the original for 7pm and we were the only ones in the restaurant for an hour. The place didn't get hopping till we were leaving around 9pm or so. This was our first night out in Prague, so now we know to eat a bit later.
I started with the terrine of foie gras and my wife with the potato soup. Both were fantastic. My main course was medallions of wild boar and my wife had the trout. Mine was definitely better than her's; stick with the game here. Desert was solid with Czech crumpets and apple strudel.
I didn't pay a ton of attention to the water bill, but the entire meal with wine cost us less than $150 US. Would definitely recommend it!