I know with early server start there are naturally going to be tweaks and such to classes and features, everything has been pretty fun to explore and play so far. But I think overall at lvl 50 the main issue seems to be what I call "surprise" damage from mobs. Basically we will be in an area with all blue mobs hitting for say 10-30 damage each, fine. Then we get more yellow and orange con mobs and "surprise", they are hitting for 500-800+ damage each (Undead Hell with the Zombie and Ghoul mobs just past the first gate). Casting mobs seem to be the worst, like the drakon caster mobs in Avalon city, again, the melee entrance mobs that stun and poison seem well balanced and a decent challenge, but then if these mage mobs have a chance to cast on you it's like 800-1000 damage per nuke.
The epic bosses in Ice Hell are all fine, great challenge. Seven Deadly Sins we did yesterday and Gluttony was hitting us for no lie; 20k - 60k damage. Simply impossible :\ Lust we killed, she seemed to be a great challenge, but we only got a stupid horse mount for her drop after 20 minutes of fighting haha. Could those Seven Sin bosses have at least a guarantee 1 item drop all the time and maybe a chance for up to 3 items total? The dungeon is hard, would make it well worth it.
Cow Hell I gave up on, the mages there nuke for over 2K damage.