I wonder if there's an easy way to set up something similar to an 'Apdex ' for CF - or some kind of metric to measure 'frustration'.

Essentially you'd need a good way to audit out the types of events that identify user behavior (dying, regearing, leveling, practicing, farming, empowerment praying, etc) - then assign an pseudo-arbitrary weight in terms of frustration to each one. Then you could narrow down common QoL concerns in an entirely objective fashion and tweak to match the profile you're looking for.

It wouldn't be perfect of course but I think it'd be a really interesting sort of thing to set up.

I also think it'd be cool if there was some kind of 'exit polling' we could incorporate - but that'd probably require you to have some kind of account that is shared between characters (which...might be fine...it's not like you can't figure out who is playing whom).