The concept does seem solid, but the balancing and bugs really affected the experience to me.
On my first try I couldn't understand why the acorns would take so long to shoot and even then sometimes they'd just disappear with no explanation, specially after the second or third day. I also didn't get why birds seemed to have such a longer cooldown on them if they were 4x as expensive, they just didn't seem to make quite a difference at first. Most enemies got through me pretty easily and I lost on day 4.
Then, on my second try, I understood I had to place the first few shooters more strategically and then put a giant amount of them around to make enough damage and have an overflow of acorns in my balance. Then I put some of the things that slow down the enemies around and, lastly, spammed the arena with birds. From there, it seemed like there was no challenge at all, I got to day 9 but it felt really pointless to go much farther than 5 (and there being no fast-forward button also made it slightly more tedious).
Overall though, the art is pretty good and, other than bugfixes, the main thing I guess the game could benefit from is just more work on general polishing and game feel, like showing a health bar for the enemies, sound effects etc. I may be biased for not playing a lot of games of this genre, but I sincerely felt it ended up lacking fun, mostly because of the stuff I mentioned. Still though, congrats on submitting, the skeleton is definitely there and I hope the feedback does help you improve it in any way!