I completed the first location (Meadow?) on Hard difficulty with the Archer. I liked the Knight but it was very hard to play the Goblin boss. Even if I played carefully, it took a very long time and I got bored and died. Soldier is great, good all around. Helpful for learning and facing new things. Archer is still my favorite, though because I love the Skill Amp synergy and developing her movement speed (more fun than perfect positioning, in a way). By the time I had exploding arrows and 430% skill amp and some pretty high damage (close to 100) I just got the healing dodge, beefed up her stamina and exploded everything to the end.
This game is wonderful. I feel that the Goblin boss takes a long time to defeat. However I understand it is also basically the end game at the moment. Maybe it's good to taste the patience.
I look forward to new characters and locations. For now, I just unlocked a ton of stuff with achievements, but I stayed up too late just to beat the game so far! I'm going to play more tomorrow.