Addictive game.
1) I could not feel any significant difference among special pegs and balls besides cosmetics. Bomb pegs don't seem to do anything besides cosmetic explosion.
2) I bought all upgrades. I felt a good balance and progression.
3) Game's motiff could be better utilized. Goblin dropping humans is funny, but it seemed underdeveloped. Nothing else calls back to it, besides Goblin seller for upgrades.