So far I've played mostly Shadowblades and Mages with a sprinkling of the warrior classes. For now, I'll just comment on my experience with Shadowblades, and here are some thoughts so far:
Shadowblades start pretty weak, but once you get enough +attack and a dwarven-steel dagger, things really start to pick up. Their melee capabilities are incredibly impressive, with stuns from dual-wield, dirty fighting, and amazing single target damage in flurry. Sweep and Whirlwind have excellent damage and utility as well.
Defense is a problem, as I don't notice many attacks missing despite defenses of more than 20. Don't know if this is something to rebalance, or actually gets pretty powerful at even higher levels. Along these lines, HP isn't terribly shabby, but I've met many instadeaths from brutal traps taking off more than my max hp in one shot, skeleton warriors getting a ridiculously powerful stunning blow off, skeleton master archers pwning me with anything, getting critted by the shade of angmar etc etc.
Magic, especially starting in the sandworm layer, is *critical* for survival. My first Shadowblade over level 10 actually found the blood of life--and died the first time to suffocation. That same shadowblade later got smacked from 263 HP to -33 HP in a single round in Tol Falas by a regular skeleton warrior. Sense is an absolutely important spell to tell you where the ranged enemies are, identify is very nice to have, and vision is also very nice to have. Of course, as I'm trying to crank Dex for more attack power/accuracy/wielding more powerful weapons, getting enough "spare" points to pump Magic can be difficult. This does indeed add to the diversity to builds, which I enjoy, but to get Sense/Identify/Vision, and adequate trap disarm probably takes around level 19 or so, and would take an amazing amount of patience.
Now, I would have no problem with the time spent to get to level 19-20, except for the extreme danger pretty much any player faces (except for a mage perhaps, but even then)--one mistake, ONE, and your life is forfeit. The shadowblade that went from 263 to -33 HP in a single round by a skeleton warrior was a real eye-opener, as I had survived numerous clashes with the elite archers/warriors/wights/vampires/The Master, pretty much all without dying. Is this a feature of gameplay that is intentional, or will be perhaps rebalanced? With permadeath as the standard (which is one thing that keeps the game exciting) I feel that instadeath should be a RARE occurrence, and not the norm. Right now, the majority of my characters have died within 1-2 rounds of getting damaged. As the furthest I've gotten is Tol Falas, I look ahead with trepidation to the event that takes place afterwards, no matter what character I'm playing.
So all in all, it's been very fun, but I think the danger should really be toned down regarding instadeath from certain common enemies like skeleton warriors, and traps.
If I'm not feeling so lazy later, I may add to the bugs section, but for now, I'm gonna play another Shadowblade

Thanks Darkgod, and here's looking foward to new improved versions to kill my precious time with!