Cool wave game! I got to Wave 56 before it got repetitive. I have several suggestions; I'll list them below to avoid large chunks of text.
1. I'd suggest mapping the direction of the attack to the direction where the player click rather than the direction the player is moving, as this is more intuitive for most players. In Unity, this can be accomplished by checking where the mouse at the moment of click relative to the player (in Unity it can be done with Camera.ScreenToWorldPoint(Input.mousePosition) and substracting the player position from it). From the current control scheme I like that you can kind of dash through monsters effortlessly by just spamming click while moving in their direction, but that gets repetitive fast. You can try having two different control schemes and testing it with people while you watch them play and take note of which one makes the game better and/or more intuitive to them.
2. Sound! Sound effects and background music can better the game A LOT. And I mean, A LOT! More than you'd think. I'm guessing you didn't have enough time to get them, but even really basic sound effects are usually better than no sound effects. Getting fitting background music is a lot harder and it can often harm your game when not done at least partially right, so be more careful with it. Done right, however, it'll give you mad mood points.
3. I didn't quite understand how upgrading your weapon worked. I think I attacked faster, but after about five upgrades changes were barely noticeable.
I'm not writing these suggestions to discourage you but to help you the best I can to improve! You made a fun game, be proud of it. I see lots of potential.