the difficulty is pretty high, but not too high i dont think, it gets difficult enough to put you on edge. what i didnt like about it was there werent enough upgrades to suit my needs, and the levels start out too intense too soon. i got bored fast due to the repetitive waves and how long it took to get to the enemy, but i could see this being a decent game, it deserves at least 4 stars.
protip: dont buy freeze bullets.
regardless of the blindly raging comments (spawns on top, shop button, problems already addressed) the game is poor, the health should never increase that much in cost, one wrong move makes the game near impossible to move on, and theres no point in playing other than to try and max out the upgrades, which isnt happening any time soon.
This is an excellent game, regardless of the shortness. It provides challenging game play with reasonable weapon distribution and constantly moving gameplay. I barely survived, and then I got owned by the bovine. Very Nice!