A couple more...
8) Do your math properly! If you're going to have 1 survivor give a 1x bonus (ie, not give any bonus at all) then the 0x bonus for no survivors needs to eliminate the score. Or, a better option, would be having a survivor give a 2x bonus and scale up from there. It seems stupid that actually managing to squeak through a "win" and get someone into the safe room barely gives any bonus whatsoever (basically just their health bonus).
9) Stop with the needless "team balancing", or whatever it is. Again, many times have I joined a game with a friend, played a few rounds with them, and then got switched to the other team. The point of me playing was to play WITH my friend(s), not against them. I can't see a valid reason to move someone to another team when you've only got 8 players - it's simple enough to wait a bit, and someone will join to balance things up again.
10) Which brings up... Allow me to select my player when joining an existing game. If I'm joining to play with a friend, and there's a spot on his team, I want to choose it - not the other team.
11) Adjust the end-map scores. It's pretty stupid that a team that barely manages to reach the radio (and then dies) gets the exact same amount of points as a team that successfully fights off all the waves and dies at the last moment.