First of all, thank you all for the feedback. It was very helpful and it allowed me to make Bodyville more dynamic, balanced, and fun than it was before.

What was changed: - Camera: it is now much faster, and it can move diagonally. - Units: I overhauled the selection mechanism. Now, you left click to select, right click to set a destination. - You can now select multiple units with Left CTRL+Click! - Macrophages are now moving much faster, and they are able to actually catch up to the invaders. - Macrophages can now chase an invader that comes too close to them. No more idly sitting around while an invader literally brushes them. - Macrophages now divide after eating 10 invaders. This was done to improve balance. - A wave of invaders is now 20 invaders, not 6, per spawn point. There are a total of 4 spawn points, you start with one, and with every wave, an additional one is unlocked. This made the game more intense, but beatable. - An in-game tutorial was added.

Play Bodyville here: https://ldjam.com/events/ludum-dare/45/bodyville. The original version is still available.