I actually enjoyed this one. The concept is neat and the execution is great too. Some puzzles were hard but not too hard.
One critique I may have is that on some levels I wasn't sure if what I did was the intended solution or did I broke the game. For example on the level with 3 bomb-arrow, 2 goo tunnels, 3 goblins and a knight I won without using the third bomb-arrow.
Overall I loved the game. Not too short, not too long. Could be expanded into a bigger game though ;)