Let me preface this by saying I'm a bit of a backpack/bag addict. I have a bag for just about everything, each with its own specific purpose. For what I use the Index15 for, it's perfect! This is my go-to light day pack and packable daypack for longer backpacking trips. For city use, I use my Fjallraven Kanken so this is the one I grab for more technical use. The compartments are great! There's an internal pocket for a hydration bladder or to keep your water bottle separate from your other items. In my case, that's crucial since I usually carry a camera and don't want it to get wet from condensation from the water bottle. There's also a small, internal zipper pocket that holds my phone, sunglasses, etc. without crushing them. The larger external pocket is great for snacks, sunscreen and things I want easily accessible.
The straps on this are basic, thin, nylon straps but distribute the load perfectly (but really, how much load is there in a 15l pack). The weight and packability of this are a great feature, but while wearing it it somehow manages to have some structure.
This pack is replacing my older Cierzo 18 (the one with the cinch top). This new, fully zippered closure is more confidence inspiring and should undoubtedly keep moisture out better.