I thought it was worth coming back and elaborate what it was about the Castles and Crusades system that really caught my eye. Mainly because it was my biggest misconception about the system the first time I ever looked it over.
It is called the SIEGE engine. Each class has a primary ability, for example a rogues primary ability is Dexterity. The player gets to choose a second primary as well. This is a level of customization to show aptitude. (humans actually get to choose a third as well.) All other ability scores are secondary abilities. The difficulty of different actions have a difficulty based on what ability is being rolled on. 18 is the difficulty if you are rolling on a secondary ability. And 12 if you are rolling against a primary.
So for example if our rogue with a DEX of 16 (+2) wanted to use his move silent skill (move silent-Dex). He would be using a skill linked to his primary ability. So the starting difficulty would be 12, this could be adjusted by the DM up or down based on circumstance. So he would roll a D20, Add ability adjustment (in this case +2) and try to beat a 12. The difficulty will also be adjusted for difficulty. Most rolls also get a bonus equal to the characters level as well.
I personally think this is genius. Its skills without a huge skill system.