This book describes the core mechanics of the Burning Wheel RPG, and its a fascinating read. The Beliefs and Instincts, in particular, look like a ton of fun.

Idyll could work for one-shot games, but (despite being advertised as a "romantic fantasy" rpg) it doesn't add any innovative mechanics or advice. On the other hand, the sample adventures would probably be fun to play out (with any system, really). The sample adventures might even serve as helpful examples (to newer GMs) of how to structure a good mini-adventure.