Very enjoyable. 5/5. Of course we would like to see tons more of the same stuff. :) More upgrade clases. Deployable shields, repulsor bullets, multiplier combos, bullet hell bosses... and hats.
My only regret in this game is that you can't always have a look at the whole screen while aiming. Sometimes my shots will land out of sight making it more a leap of faith than aiming.
In addition to all the other comments I'd like to remark that the game needs a short period of invulnerability after death. Curently, running into a tight volley of bullets makes you instantly loose all your lives.
Controls are in need of customization. Trusted WASD scheme abandoned. Shooting in angles is tricky, jumping looks and feels awful, put some more time into this and this might turn out really well. Good jb so far. ;)
Same weaknesses as the previous Zombotron titles... and some more. Coins rapidly disappear if you are re-spawn in an insta-death situation. Re-spawning takes you too far from dead friend or hard to reach chests. At other times it takes you exactly to your death again. Friend starts fistfighting a boss, dies and trhe body gts trapped behind the boss. Armed enemies hurt you before you see them, sometimes killing you from off-screen. Controls, mostly jumping is unresponsive when a lot of action is on screen. Most lost battles are lost because of terribly stupid friend AI. In-level-checkpoints are not in place, you have to re-grind a long level because of mistakes. Most of this was already true for previous Zombotron games and should have been addressed by now. I can only evaluate the first 9 levels because my friend keeps dying behind the boss and I can't reach her and complete the level. With every frustrating level restart this game looses a star. :)