I have Ortlieb backroller plus bags. They are clearly designed for long tours, and if I was designing a bag for commuting, I would make many changes. Weight or looks would not be big factors for most commuters. It's mostly about function.

They should be waterproof; Ortliebs win on this one.

They should clip on and off the bike simply but securely; another win for the Ortliebs.

They should close simply and securely; fail for the Ortliebs.

They should travel well full or empty, as you may leave out empty to fill with groceries; fail for the Ortliebs.

There should be no loose straps; major safety fail for the Ortliebs.

They should be sturdy; possible fail for the Ortliebs.

An easy method for locking them to the bike would be a plus; Ortlieb does have a lock available.

Check out the Topeak MTX DXP rear back with panniers. It's a clever system with panniers that roll down when you need them, and store in the bag when not in use. It's a great idea, though it would be a lot more useful if the panniers were bigger and sturdier.

Lots of internal pockets for tools, tubes, cell phone and such would be a nice touch; at least one of them should be padded for cell phone, Ipod, etc. You could put things in the pockets that you want to carry on every ride, and keep them segregated from the groceries or clothes you loaded up that day. The pockets not much good unless they hold the items securely.

Reflective tape or paint on the outside of the bags is a smart touch.