Each category will be scored from zero to two; zero being abysmal, one being acceptable, and two being exceptional. This will result in a total between zero and twenty, zero being a failure in every possible way and twenty being as close to product perfection as possible.
The underlying concept of a product. Sometimes something is a great idea on paper, but fails in execution. Moreover, good looking products are far better than ugly products; as such, this category will evaluate aesthetics, too.
What's used in the construction of a bag is particularly important. A great design can be quickly ruined with sub-par materials. Of course, depending on the particular use of the bag, materials will differ.
Snaps, clasps, zippers, and so on. On many bags these sorts of things fail far more quickly than the fabric or stitching. Of course, they're often the most irritating to repair.
This is mostly a metric of quality stitching. There aren't many other ways to hold fabric together...
How easy is it to pack the bag?
How easy is it to retrieve things from the bag both while it's on and while it's not.
How many pockets does the bag have? Where are they located? Are the pockets of the variety that one might expect? Are they as useful as they should be?
Modularity / Expandability:
Multi-use, multi-function bags are wonderful.
On pouches and other such accessories this subcategory will be scored based on the attachment system (e.g., MOLLE, or what have you).
Unnecessarily heavy bags are bad. Lightweight is generally better. I'll try to evaluate the weight of a bag based on its class.
Strap design, handle design, back-plate design, etc. All these weigh heavily in the comfort of a bag.