Totally Agree!
It can happen. I am starting to believe that a #1 factor in the game is the spawn cards. They can royally screw you and make the game extremely tough or it be a cake walk. There is really not way to tell. In the same session we followed out normal tactic of opening buildings....all or as many as we can at Blue Level. It usually works. BUT when we opened the third building we had the worst spawn EVER. Not only Abomination, but manhole covers and it was just timed where nearly all the manholes on the board were "spawn-able". It exponetionally increased the number of zombies on the board.
For sure, the spawn cards are the one thing that can ruin your day. I've played mission one 9 times so far with only one victory by the skin of my teeth. In every loss, I was suprised with unanticipated spawns cards giving extra turns of sewer spawns. I love it though, cuz you start to count cards as you play, wondering if it'll happen this turn or the next. I've also recently employed opening buildings in the blue, but it's not fool proof. I've found that when opening a building in blue or yellow, you should be in the best tactical position possible, even if you burn a turn moving survivors.