Enthusiasm!
This is the best point and click defense game I've ever played.
I liked the fact that you aim by using both the keyboard and the mouse, so that it's not all just mouse--crucial because I'm using a laptop.
I liked the graphics and fog and sun.
I liked how it's not so difficult. The focus is on experiencing the zombie attack, not on making it through impossible frustrating hordes.
I died once after level 2 and I like how it gave me the option to retry.
I like the characters and the collection of a party of compatriots.
I like the other touches like the journal entries and the placement of the weapons on the board.
The only thing that might improve it (emphasis on _might_) is if you added a little more variety in what the weapons are good for, to make your alternate weapon useful for something. You have that with the chainsaw but that's about it. On the other hand simplicity has its virtues and it might ruin the game style to have him throwing hand grenades or something.
For anyone who is having any trouble, what I did was put almost all my hours into searching for more people until I had max population, but repairing to keep at least 70% health, and only then going for weapons.