What factors are at stake when evaluating a curriculum?

Although there are many factors that contribute to a successful curriculum, one major area of concern is whether or not the curriculum works. Simply stated, is there a document that is easy to use, comprehensive, and realistic? Will the curriculum address all necessary information in a timely manor? Will teachers and students end the school year feeling successful and better informed?
Marzano's approach to curriculum seems to be the most realistic. He understands that distractions in the classroom along with an overload on material will lead to incomplete lessons and possibly the idea of never teaching certain skills due to lack of time. He states that a curriculum should be guaranteed and viable which basically means it's going to work in the amount of time you have to teach it. For such a basic thought, it's interesting to see how many districts overlook the simplicity of it. I fully understand the difficult task it must be to narrow down a curriculum in order to make it guaranteed and viable, but that's why this may take a few years to iron out. Constant revisiting to the curriculum would be necessary in order to make this philosophy work.