Leaves a bit to be desired
This game is a good start, though you still have work to do.
First of all, the building gets repetitive quick. I can understand wanting to take shelter in a building in this situation though staying permanently is just too much. You should be able to leave the building and go to others, walk the streets, find things, find survivors and so on. Being stuck in one building for the entire game, and a small one at that, gets old quick.
Second, I would like to see missions. Missions seem to be rare in games like this. As I said earlier, the building should just be one place in a larger city environment where you can come and go at will and travel the streets to other buildings and locations. The missions could be part of this. Maybe the entire point of the game is to get from one end of a massive city to the other where the national guard has set up a position where you will be safe or something. As you go through the city you run into NPCs who give you missions you can choose to do that will help you on your way. You know, rescue people, find a lost item or escort them somewhere. You could even use the missions to unlock certain weapons and especially to get certain types of ammunition.
Third, NPCs, you need more of them. The only other character in this game is that one woman who is practically useless. She's not exactly marksman of the year and has a habbit of walking right through large groups of zombies. A nice feature would be NPCs scattered throughout a large city who as I said before want your help. Some could join with you until they are killed or their mission is over, there could be hostile survivors, angry trigger happy looters, street gangs and paranoid cults. A story could even be told through the NPCs, especially the story of the zombie virus. I saw hints of a story with the only other NPC in the game who I could not unlock and that seemed interesting, unlike much of this game.
Third, weapon selection is crucial to a game like this. The selection is acceptable, though could be better. I see no melee weapons and while not the best choice for a primary melee weapons can save vital ammunition in a drawn out survival location, or be used to silently dispath hapless infected without drawing attention to yourself. A bayonet for certain rifles (AK, M16, WWII bolt actions) would be a nice touch. The weapon upgrades should be unlocked through missions, as should certain weapons, especially military class machine guns. Most people who own guns only ever own firearms such as handguns, shotguns, hunting rifles and SEMI-automatic "assault" rifles. Full automatics are illegal without numerous permits and are expensive to use so they won't be commonly available, even in a police armory. This fact should be included in the weapon selection. Military style weapons could be found in the hands of dead soldiers (A rarity) and if you include hostile survivors they could have interesting weapons in their posesion.
Finally, zombie variety is lacking in this game. I counted a grand total of two types of zombies and neither group was much of a threat. A few more types of zombies would be nice, especially zombie dogs, it's hard to take a zombie game seriously without zombie dogs. I'm not complaining that the zombies where too easy to kill, 2-3 shots with a mid caliber rifle (M16, AK series of rifles) should do the trick but maybe faster zombies or more muscular zombies that cause more damage using the normal zombies as shields for example.
In conclusion, you have the beginings to a good game here, though you still have a long way to go. Include the changes I recommended and this gae will be better as people enjoy a good story to go along with their zombie killing and they enjoy unlocking weapons. I won't go into how you have to buy certain things or get an account at some site as this is your game and you do have a right to do that if you wish, even though I would advis against it. Put a link to your site and leave it at that.