I got this as a replacement for a medium-sized Timbuk2 bag that was just getting too small to carry lunch, change of work clothes for my commute, and gym clothes for the lunchtime workouts. It has awesome features (internal organizer pocket, extra top carry handle) that would cost you close to $150 if you got them custom-ordered in a Timbuk2 bag.
First, the size is great - it is VERY large, which means that when it's not quite full, it still wraps around my body well enough to feel secure and not place any pressure points on my back during the ride. I also like the extra pockets that keep me organized - the external pocket on the front flap helps stash a pair of gloves and a beanie, the pocket across the back can hold my day planner and file folders, and the end pocket is awesome for quick access to my wallet, keys and cell phone.
I haven't lugged my laptop in it yet, but the padded pocket is as good as anything I've seen in a messenger bag. I've had it out in 30-40 minutes of pretty continuous rain, with the inside staying dry, although I'm not sure I would trust anything in the external pocket on the top of the flap. While water resistance has proven to be acceptable so far, if you're looking for extreme water resistance, you're probably better off with the rubber-lined Timbuk2. The internal lining is light-colored, which is a huge improvement from by black-lined Timbuk2.
The only problem I've had is with the (excessively long) strap slipping. It seems like the smooth, flexible seat-belt type material used for the strap is not thick enough or have enough "bite" in it to stay "fixed" in the strap clamp. Since I love the whole bag so much, I found a quick and easy solution that does not alter the bag permanently - I wrapped duct tape around the strap just under where it threads through the clamp, and then re-threaded the strap through the clamp. The duct tape thickens the strap, provides a bit of bite for the clamp to sink into, and also stiffens the strap under the clamp, so that it won't travel through the clamp quite as easily.
It's a very-well engineered bag. This would be a five-star review except for the strap problem. Since it is an easy and unobtrusive fix, I'll go with four.