The existence of fetch/kill quests aren't bad. It's when they're thrown in for seemingly no other reason than to pad out content length (Moogle, Gnath), or when they're the only kind of quest in the zone (Azys Lla), that it becomes frustrating. It got to the point where I would enter a new zone, see a new kind of monster, and sigh because I knew I would be killing 4 of them for an NPC.

Exploring for the aether currents was fun. Having to guess which side quest chain had an aether current hidden behind it was not.