Quick review: its a little flimsy if you want something that has more structure this may not be for you. Other than that the halcyon fabric is strong, lightweight, and fairly water resistant. Great as a packing cube when going on a trip, as a side bag its also great to throw some stuff in and get going.
Longer review: I don't trust any other backpack brand as much as Tom Bihn. I am addicted to backpacks and I will always save up for Tom Bihn because they last forever which is helpful for your wallet in the long run and for the planet because you are not wasting cheap backpacks in a landfill somewhere. The halcyon fabric that is used on this bag is amazing. Strong, ripstop, colorful, and looks timeless. My wife was going to buy a cheap backpack on Amazon and I had to explain Tom Bihn to her. She fell in love with the brain bag for college and travel. After seeing her with one I had to grab one for my work. We have been buying accessories ever since. When I saw her constantly carrying a fanny pack we had as a small purse I decided to pull the trigger and get her this bag in her favorite color purple. She was excited, but once she started using it it doesn't leave her side. I got her some mystery organizers to clip onto the O rings inside and it makes it even better. Now I am waiting for a Freudian Slip for the brain bag and she will be set.
Summary: If you are into quality, fashion statements, and awesome bags buy from Tom Bihn and you will be set for life.