Nice! I like it a lot better with weaker/faster zombies. It feels more like an action game now. I don't know if this is what you would have in mind for this game, but if you added a money system with upgrades you can buy, I think the game could be more popular. You could keep the achievment upgrades, but maybe add many more weapon/armor options that you can buy with money. Also, maybe power-ups that spawn from boxes/barrels that you destroy, such as brief invincibility, no weapon heat up for X seconds, speed bonus, etc. People here love to buy upgrades in games, so I think that would make your game very popular.
I haven't played that much into the game, but so far my impression is that the levels are too long/boring/repetitive. I think either cutting down the number of zombies per level, or make them die more easily. In this kind of game you want to slaughter mass numbers of zombies somewhat quickly (the weak ones anyway), not run over one about 5 times to kill it.
I love that we can just hover and type in numbers instead of doing all clicks. It certainly needs more puzzles, especially more challenging ones. If you could design a system to make random puzzles, that would be excellent. As others have noted, the sequence to go through after completing a puzzle could be shortened. Overall, it's pretty good. 4/5