Just watched Zackavelli's stream on this and here are my thoughts:
- I can't remember if the stream muted your game, but SFX (just a simple shoot, hit and death sfx) would be huge
- While the art looked good, definitely spend more time testing (e.g. what happens if I place no gnomes). A super easy one that could've come from this is 'restart game automatically if any zombies get through'
- Too much text for the tutorial - have a quick look at how Plants Vs Zombies does it - it's just one sentence at a time in between letting the player take actions. Generally, the more text you have; the faster they'll skip through it!
- Overall, pretty godo game for your first ever finished project! Well done