The awkward distance between the cursor and the actual target can be annoying; that red dot is small and hard to notice. I ended up clicking the "Zombie Games" link because of that.
Also, do the zombies look like they're dressed for a party parade to anyone else? Those torn jean shorts just look more like a fashion statement than the results of a chaotic zombie invasion.
Pro - I can distinguish between the different objects - zombies, weapons, building, etc. Everything functions correctly - Weapon fire, reload, zoom, weapon change. The music is good. Maybe not the best for setting the atmosphere of a zombie attack.
Con - Repetitive. Reticle/Red Dot is hard to see. Links hinder smooth game play (kept clicking FREEGAME.NET link while in sniper mode).