So I've finished my game for the Ludum Dare contest. Today I spent a few hours fixing my graphics to not be so shoddy.
The buildings don't really match up to the scale of the characters, though I'm not really worried about that. As for code changes, I gave both the zombies and player simple momentum for knockback when being hit. For the zombies, this also helped smooth out their movement. I've also put in some simple particle effects on damage. The effect shoots out 10 colored balls which fly out in a random direction and slightly up. They have basic gravity and will bounce when hitting the ground (z=0). For the zombies, I colored them a stale red-near brown. Donuts emit brown, and the player red. This gives a nice effect and really does make the game more interesting. Another small graphical change is that characters turn more red as their health goes down. This is more visually stimulating than modifying the alpha.
A larger update added today is a melee attack. You can see from the screenshot that the character is holding a rolling pin. If zombies get too close to the character, he/she can right click the mouse to swing which will hit surrounding zombies and push them back a bit. This is nerfed to reduce players' attempts to rely on it though, by limiting the speed to 1/5 of a second and only hitting ten zombies(this also reduces some sound effects clutter as I didn't build a sound manager of any sort so sounds are played for every action).
As for optimization, I gave the zombies a timer to stall updating the field which is staggered among all of them. After the initial delay, it will reset to 5 ticks on each count down. This way, with 50 zombies on screen only 10 or so will attempt to update the field at any tick. Adding this did not seem to harm the zombie behavior, and the game no longer crawls after throwing many donuts. The targeting has also been optimized, before they would attempt to update the field for each available target that was close. Now they find the nearest object and update the vector field based on that object only.
All in all, I believe the game is a success. It started as a quirky game with some interesting developmental elements, i.e. vector fields for AI movement.
Almost forgot links to the game.
OS X application
For linux, grab the source and install Ruby+Gosu as per the README (unless you already have it)