Alternative gamemode maps! Go!
This is sort of like a CTF. The portal teleports you back to base and adds 1 point to your team's total. You'd play as a team of 2-3 maybe. and the ammo in the upper corner rooms respawns. You play until you get 5 points, as the zombie spawn rate increases. doors and keys respawn after every point. basicly, it's 5 maps in a row, that are identical, except more enemies spawn faster each time you advance. maybe add a boss battle at the end. It'd be designed for the online capabilities (We're adding that, right?) and co op gameplay.
LET spawntimer = 5 //time between enemy spawning
LET enemylimit = 30 //enemies per level
LET maxenemy = 10 //maximum amount of enemies on-screen
LET line$(1) = "11111111111111111111111"
LET line$(2) = "1aaaaaaa100a001aaaaaaa1"
LET line$(3) = "1Fdhaaaa1010101gdhaaaa1"
LET line$(4) = "1L0000b100101001b0000L1"
LET line$(5) = "111T1111U11R11U1111T111"
LET line$(6) = "0000000001K0p1000000000"
LET line$(7) = "0000000001haa1000000000"
LET line$(
= "00000000011111000000000"
LET line$(9) = "0000000000zzz0000000000"
LET line$(10) = "00000000000000000000000"
LET line$(11) = "00000000000000000000000"
LET line$(12) = "000000yyy00000yyy00U000"
LET line$(13) = "001R10yyy00000yyy01T100"
LET line$(14) = "011h1100000000001110110"
LET line$(15) = "0109010000000000100K010"
LET line$(16) = "01111100000600001111110"
LET line$(17) = "00000000000000000000000"
So, we should focus on not only the story mode, but also on having vs. and co op online modes. I have some ideas. Another idea is called "Hold the fort mode" where zombies keep coming and if they get to your wall they deal damage, so you have to keep them back.