Great stuff, and there's a surprising amount of content there, with the weapon upgrading to a next tier. Really liked the progression with the waves and the ability to try harder waves. Did not get the appeal of towers at first, but later realized they are life-savers. Still didn't get the wall building mechanic since they breat too fast, but oh well.
Large enemy fatality is VERY cool, discovered is by accident and tried to use as often as possible.
My only complaint would be the lack of tutorial, I guess - would've preferred to know about big guy fatality way earlier - could've saved my first couple of runs.
The upgrade and weapon variety is a lot of fun, though some weapons (like the crossbow) seem too situational, while others are way more useful (like a shotgun or a rocket launcher).
Great stuff, really enjoyed it!