sorry, I haven't checked this for a while. Wow. Looks like you've made progress. Sweet title screen btw.
Weren't we going to make a boss battle level? The code would be simple enough, just add another type of zombie with way more health. You could go on to make a big hideous mess of green, rotting flesh sprite, maybe make little zombies spawn from it to distract you, and make the portal appear when you kill it.
If you need ideas for levels, I can help, but when it comes to actually making them, it turns out I'm not very good. I made a Pac-Man level, 4 zombies in a middle area, walls forming a maze, power ups in the corners and ammo in every blank space. Sadly, this was too much for SC to handle, so I got an error message.
Also, this game has potential to do great things. With what we have so far, we could expand it into something much greater. A complete single player campaign with a storyline would be cool.
A survival mode, could be made by adding a timer to a level, making ammo/bombs/armor spawn every once and a while, after maybe 10 zombies killed you could get the better gun. Or maybe you just get rid of ammo entirely and give the character a machine gun that overheats if you shoot it too long. Or a store menu, where you spend points you get from killing zombies on upgrades and ammo, and bombs.
While I'm throwing ideas that will probably never happen out here..... ONLINE MULTIPLAYER! CO-OP CAMPAIGN!! MELEE WEAPONS!!! SNIPER RIFLES!!!! MINIGUNS!!!!! PLAYER CLASSES!!!!!! BONUS LEVELS!!!!!!!! EASTER EGGS!!!!!!!!!!! 3D RENDERED CUTSCENES!!!!!!!!!!!!!
*Please note that the above statements are caused by zoo's overactive imagination, and will never be expected of anyone. He seems to have blown up an impossible/highly unlikely ideas grenade.