Epsilon Strain Balance, balance, balance.
At Sector 3: Difficulty 6 now and it seems like every time I open a door, there's a zombie to poison me. I'm fine with there being poison, but there's just too much of it and even with 250 armor points and x2 armor, I'm taking 9% damage each second for 20 seconds. There aren't enough armor packs going around for me to cover that kind of damage, especially if the spitters are right in front of the entry door to return the poison timer back to 100%. There's just no dodging them.
And it's painfully repetitive. The enemies can all be taken out just by running circles around the room with scatter shot.