I play on classic and did not noticed quest bugs or too hard fights in driftwood.
I would say fights seem to be a little too easy, because there is no chess like feeling where almost every choices of your moves are important, so you must really think what to do next.
I remember some fights with few levels higher enemy, for example when I arrived with level 9, I had a fight with level 12 magisters when I tried to cut off Meister Siva.
I believed that might be tricky, but no, fight was challanging (had to think what to do), but not hard in practice.

I think there maybe is a problem with balance of your characters development and whole party?
Also, it is turn based tactical game, which means you need to think about strategy tactics.
- Take surfaces to your advantage
- Do not spread your attack to all, but eliminate one by one, so you eliminate faster the sources that damage you
- Remember you need to pass enemy armors first to be able to use effects or reach direct damage, so use physic attacks on enemies on weakest physical armor and magic attacks on weakest magic armor
- Keep an eye on your armors, and recharge both with skills or spells as soon as they are too low, and take this as higher priority than attack (otherwise you might be disadvantaged with special effects, direct damage and even lost moves)
- Mix spells (wet(rain)+chill(water damage spells) or wet(rain)+shock(air damage spells) will make your enemies to lost turn)
- Summon creatures right behind enemies (higher damage when backstab or side, and extra opportunity attack if enemy wants to move to your characters) to make them busy instead of you or spam totems (there is no limit like for creatures)
- Use teleport to move out (as far as possible to make lost AP for move back or bring him directly to proper character that will handle this one in best way) more dangerous enemy or protect your character in critical cases (safer area)
- Shields are good thing to have, even for casters (much better armor stats, option to recharge physical and magic armor, nice damage and area of effect and range with shield throw skill)

The only real balance problem I found are Voidwokens.
The seem to be most easy enemy (mostly no armors or weak armors - waiting for your area of effect spells and spell combos (knocked down, stunned, frozen) that will make them lose a turn) and a lot of experience (too much in my opinion).

As about skill system, I like it very much, and I found more than half of them very useful (some when used as combo with other skill or spell).
You can still invest skill points above skill books requirement to get better damage (or other advantages), but on other hand there are a lot of skill schools that you can start invest too and even later (thanks to skill auto level ups so they not go weakened later and no pre-skill requirements) to get more possible options during combat.

It is very well designed and thought game, but just different than others you may know.
Compare it to other good games like Baldurs Gate, Planescape Torment, Temple Of Elemental Evil, Wizardry 8, Dragon Age, Jagged Alliance 2 or other in some way similar games, and still tell me it has less to offer.