Concept: 5 out of 5
Execution: 4 out of 5
Yeah, but: It does exactly what it's meant to.
The Long Version: Think Tanks's Glass Taxi is a backpack designed to hold a camera and long lens, with room for a small number of extras. There's no room for anything else, though, with only a small mesh pocket to hold accessories. The pouches on the side are tight to the side of the pack to securely hold a tripod or monopod, but do not stretch to hold a water bottle or have elastic to retain small items.
Build quality is very good, easily matching or beating the construction of my various cases from Domke, Petrol, Manfrotto, and Crumpler. The self-locking zippers are a brilliant design feature, and they and all of the metal load-bearing hardware have a dulled finish that's understated and will wear well. The included tripod straps have a velcro section that mates with hidden velcro underneath the side lash points, holding the straps securely in place even when the snaps are undone. Think Tank also includes far more dividers than are shown in the photographs on their web page; there's certainly enough to use this backpack to carry a complete system of small lenses and accessories if you choose to.
My typical load for this backpack is over 10Kg of camera, lenses, and tripod, but it carries it well. It doesn't counteract the effects of gravity, but during a six-hour shooting hike the pack never became an issue. Its long and narrow profile doesn't interfere with movement, it's easy to move through crowds or hand-carry on public transit, and it sits upright when it's put down. Comparing this pack to my other backpack is an extreme contrast: I love my Glass Taxi as much as I don't love the Lowepro Micro Trekker.
I may have my bag under-loaded. Because it's designed to hold very large lenses, it's boxy and deep. This means that there's a lot of movement when a tripod is attached to the side of the bag. I've solved this by adding one of the monopod straps (which don't have the snap buckles of the tripod straps) to the carrying handle at the top of the bag.
The only real flaw in the design of the pack comes in an unexpected way: insufficient velcro. Think Tank makes extensive and intelligent use of this material everywhere except for the small mesh accessories pocket on the inside of the lid/front panel. This is the only place to hold small items -- large ones won't fit in the flat pocket -- such as spare batteries or cards. However, when the bag is laid flat and the lid is completely opened to remove a secondary lens, the opening of this pouch is upside-down. There's only one small patch of velcro to secure this pocket, leaving plenty of room for the contents to slide out. I've solved this problem by keeping a second bag inside this pocket to hold my small items, but there's simply not enough room to spare for this to be an effective long-term option. Given the thoughtful design of the rest of the bag I have to assume that there's a good reason for this deficiency, but I don't see what it might be.
I'm not sure if this is my favourite bag; my Domke F6 has a special place in my cupboard after it faithfully got me through a three-week world tour. But after a tragic purchasing decision, I've spent a lot of time looking for something better before I bought the Glass Taxi based on the strength of Internet reviews. I wish I hadn't wasted my time and money and had just bought this one at the very beginning.