Messenger bags are notoriously uncomfortable, putting all the weight of your gear on one shoulder. The Think Tank Retrospective bucks this trend with a well-designed shoulder strap. This bag is all about the little design tweaks that end up going a long way. For example, the velcro pocket tabs can be folded down--essentially, this makes getting your gear out silent, and anyone who has every undone velcro in the middle of a wedding knows just how important that feature could be. The interior dividers are customizable, two exterior hook and loop pockets can hold an extra flash or small lens and the exterior flap has enough room for an extra body or smaller accessories. The bag can also hold a 10" tablet or 11" laptop.
While comfortable and well-designed, the bag's construction is not waterproof. There is a rain cover included that protects everything but the strap, but it's worth noting there are waterproof bags that don't need the rain cover. Some may say the bag is small, but the capacity (DSLR, two lenses, a flash and a tablet) is a good size for keeping a one-shoulder bag comfortable.
The Think Tank Retrospective is a comfortable messenger bag, which is hard to find. For that, the bag will cost you around $150, which isn't obscene, but is higher than many shoulder bags with a similar capacity.