Aria had an odd die mechanic that required calculating your target on the fly. I could dig it out and describe it exactly, but there's not much point.
Character creation was very interesting, but it took a lot of work to get going, and the sixteen stats didn't help much.
On the other hand . . .
The text of the books is, shall we say, beautifully written. It's so beautifully written and throught provoking that reading a few paragraphs often caused me to sit back and think, not in confusion, but in inspiration about ideas and peoples and places.
The sections on world building and interactive history are great.
Aria Worlds expands heavily on the world building sections in Aria.
The artwork on the cover and interior was excellent to great (for my tastes, anyway).
The book was, however, badly in need of a second edition that revised the basic die mechanics, and tightened up character creation substantially. It also seriously needed to tighten up combat mechanics descriptions, as well (yes, the books were a little over-written).
It also had a framework to create custom magic "systems". They were all based on the mechanics of the game, but where the magic came from, how you cast spells, etc., could all be customized (sort of, you have to read it to understand).
It's the interactive history sections, including the parts where PC skills can be rolled to effect histories and the politics of nations, that you'll be most interested in.
