Fun, but not user-friendly
First off, I just want to say that this was a fun game for what it was -- a typical 2D zombie shooter. And it kept me coming back for more, which is what a good flash game should do. However, it does have a couple flaws.
First off, as has been mentioned, the reload time is ridiculously slow -- my gameplay was pretty much 33% shooting, 66% reloading. I started to wonder if my character was perhaps lacking an arm, which would explain why he seems to have so much trouble inserting a clip or magazine :P
Secondly, some sort of description for the various attributes and weapons would be nice. Health and Accuracy are both self-descriptive, as is Speed (though it would be nice to note what kind of Speed -- is it movement speed, firing speed, etc.). However, I have no idea what Educability, Recharge (perhaps you meant Reload?), Z. Hunter, or Luck do for my character. Likewise, weapons need some visible stats. While more expensive weapons are presumably better, it's nice to know exactly how different they are -- for example, while the Uzi has a much large clip than the Glock, it sometimes takes a full third of that clip just to kill one zombie, so it's not always a superior choice even though it's a "better" weapon.
Third and final is the barricades. They feel far too weak to me, especially since there is no chance of preventing them from taking at least damage each wave -- there's simply too many zombies for you to kill before the wall starts getting hit. For the first couple of waves the barricades were completely unnecessary, but in later levels they are absolutely vital, as the zombies simply spawn too quickly for you to kill them all before they reach the antenna and start damaging it. This necessitates constantly spending a fairly sizable chunk of your money on repairing the walls. To be fair, this is true of most games of this type, but it is also something I have always hated about them -- it would be nice to actually get to spend my money on upgrades instead of having to constantly fix a pile of scrap metal.
Anyway, that's just my opinion. Like I said, it's a good game, and it definitely made me want to keep playing, but the mechanics feel a bit clunky at times. Smooth them out a bit and you could have yourself a truly addicting game.