It's hard to know what I want from a camera bag backpack, but having owned two now, I know what I don't want.
My previous bag (Petrol BPN3) was just a shade too small and had too few pockets but was otherwise very comfortable to wear and easy to use.
This one, bought because I wanted something bigger, is much more spacious internally but externally, it's very bulky. There are straps everywhere, little tags and toggles hanging off of every strap: when wearing it on your shoulders it's easy for it to snag on your clothes or even itself. The built in tripod carrier on the side is a nice idea but a bit impractical unless you have a very lightweight tripod.
Pockets are plentiful, but some are very small (almost pointless) and impossible to reach.
The main flaw is the opening. You put the bag's back (the flat part that goes on your back) on the ground, rummage to find the two main zips (which blend in with all the other zips) and then unzip the entire front which flips over itself, exposing the inside. This means, to get the camera out, you have to find somewhere dry on the ground you can put this huge bag, then hope there's an equal amount of space behind it for the door to rest once open. Doing this in the back of a car is very awkward. It also means the bit that touches your back is the bit that sits on the wet, muddy ground - not nice. If it hinged sideways like a cupboard door instead of at the bottom like a drawbridge, you'd need less space to open it.
It's got plenty of room inside and the compartments are very adjustable (with their Velcro walls) but its very bulky, awkward to open, covered in unnecessary straps, zips and the occasional pointless pocket PLUS it needs twice it's own area of space to open it! I always stuff my camera bags full of equipment and I got rid of my Portabrace CAR-3 because it hurt my back and shoulders with the awkward weight distribution; I thought a backpack would ease that, but it's really only replacing one problem with another - at least the bottom of the Portabrace bag remained it's bottom and it didn't matter if it got a bit damp, PLUS removing the camera from the CAR-3 bag was lightening fast with the entire top of the case opening in one swish of a double zip.
I'd like to sit down with Petrol, Kata and Portabrace and design the perfect backpack...this isn't it. But then neither were the other 2 bags I've owned.