My thoughts after finishing the Kindred Fire campaign:
We choose a party, that was good a killing groups of monsters, since killing many monsters quickliy is key in a dungeoncrawl like descent. So we had a Barbarian (Tahlia), a Stalker (Tetherys), a Runemaster (Widow Tahra) and an apothecary (Andira). The first one or two quests were quite tough due to the nerf of AoE attacks, but things start to pull off once the right items came out. For our Runemage it was the Staff of Greyhaven and for our Berserker it was the Iron Battleaxe. We struggled once again after the transition to Act II, but could handle the rest without bigger problems, because we got another pair of insane weapons.
The most challanging quests were the first ones in Act I and Act II. Here was the tier level of the monster significant in comparisson to the heroes. Either you have no gear and no skills at all or your gear is to weak for the stats of Act II Monsters. But Monsters don't scale with your gear and learned skills. Once you have grinded a bit, things start to become way too easy.
Our Berserker had the Hammer of Doom with 3 Attacks and Mana Weave, while our Runemage had the Bow of the Eclipse with 3 Attacks. They generated ridiculous amounts of damage.
We thought the main balance issues are not the classes but the items. Once you get those hard hitting weapons, monsters can't really defend themselvs. we played it that way, that Whirlwind and Runeblast are exausted after use, but they were still too strong. The Apothecary is definitely a powerful healer, especially the green power dice with an additionly surge is great. I played the Stalker class and must say, that i didn't have fun with it. He didn't contribute anything special to the party and since all monsters were dead after activating our Berserker and Mage it was really boring for me. His skills cost too much fatigue, so fighting with him is quite difficult. He can't generate the damage the other classes did an placing traps near to the enemies is often fiddly.
We take a break now from Descent, but we will come back to it with different Heroes and different clases and see, how things have changed.