I played a bit during the weekend. Got a Paladin to lvl50 as well as a Lich.
Paladin with spiraling hammers. Very good defensively with all the block stuff.
Lich with Spirit Plague. Ridiculous clear speed with the plague passives. Click once and whole screen dies as it spreads. It seems like anything that can apply plague is OP for leveling. Not sure how it will be late game at lvl50+. It's like Essence Drain + Contagion from POE in one click.
One thing I would like is more passive skills. We can use 5 skills but almost always have to actively use them. Each class should have 2 to 3 skills that can be converted to be a passive skill. Like proc the skill on kill/stun etc.
Every build will kind of have a clear skill and a single target skill. No need for more than that so it would be useful to have more skills that procs/buffs passively.