Thank you for the feedback! Sound is definitely something we wanted to add, but we didn't have time to find or create appropriate sounds. I think you're right, a visual effect, especially when enemies and the trees are hit, would have definitely improved the game's overall feel.
Personally speaking, as the game's programmer, I think it's easy to underestimate the importance of those details when you're trying to add all of your desired features under a deadline.
The artist of our team actually had some visual effect assets prepared that I was unfortunately unable to implement in time! Don't want to let that happen again!