After quite a few tries I managed to snag a win with a dexterity, intelligence, and strength character. I definitely found it easiest to win with the ranger as they have high dps, good crowd control, and incentives to build up a big pool of speed points. Especially they had an easier time with the first few levels (I find that I most commonly die on level 2 to normal battles with frogs or bees, then my character powers up and the 3rd dungeon and side dungeons are easier).
I found the recent change that makes the tome of knowledge grant you a free point in the skill made the game a lot more manageable, as you could afford to spec up in both your offensive skills and passive/mobility skills.
All in all this is a very good and addictive game - at first it seemed impossible but after learning the mechanics and some basic builds it becomes very doable.
PS: the comments above about the duelist being overpowered are a little bit hard for me to believe - I struggle getting past the first couple dungeons without any crowd control or ranged attacks. Maybe they require a higher skill floor.