I like the concept, but it needs a bit more content.
The knights are pretty easy to continuously kill with a couple traps at the start. Maybe have a little space around the traps where you can't put any more traps (this would avoid them overlapping as well)
The idea of the goblin leading the knights away is also pretty cool and could be used for some interesting gameplay/scenario's.
I really like the art style. Good job on that.