So far I have seen few legit complaints about dungeons.
1) Too hard for casuals who just want to experience the content. Too steep difficulty for casuals to learn.
2) Plenty of uninteresting fights with just huge pools of hp.
Making current difficulty of dungeons the hard mode (with few tweaks) would allow making much easier normal mode which would fix 1) and partially 2) (normal mode would have less hp).
Tweaking the hard mode mobs to have more skills / be more dangerous would fix rest of 2). Also to spice things up, add WP-locking during major fights and more reseting events for hardmode.