Hey! Not bad! You should pay more attention to how you explain the economy, since it's so important to playing the game. Explain that you want to fit in generators when you can, without going overboard - create levels that make the player realise this when their initial strategy doesn't work out well enough. Explain through gameplay that they might want their generators and units to tank some damage and that it's okay, and that it's fine to hold resources to react to the units that come - I think you do that a bit in the level where the first wave is 3 enemies at once.
I think you mislead players with the wall - it's a waste of resources against units that aren't the samurai. The power of the samurai is overwhelming initially since they take so much damage and deal just as much, and that can be frustrating for players who don't have a perfect understanding of the game's strategy - you should introduce them in a level where the player has the room and money to react to it. The freeze mage is too weak to be used, but that doesn't really impact the game.
There is also this trick where you keep replacing your unit that just died to stop enemy units from advancing infinitely, provided you have the economy to support it. This should be removed.