The Warden is faster. It used to be slower than your walk, so you could just stroll away from it. Now it is faster than a walk and slower than a sprint. If it is chasing you, run.
Rent is higher. A three day cycle now costs 20 crates' worth instead of 12. Your first cycle's rent goes from $1,688 to $2,813. One perfect day no longer pays for the whole cycle. Two good days will, but a bad day or a wasted one will hurt.
Toxic air is dangerous now. Breathing it without a mask drains your health much faster: about 40 seconds from full instead of 100. The air also turns toxic sooner, from the seventh crate you pull instead of the ninth, so the back half of every level needs your mask. Filter upgrades are worth buying.
Dying costs more. A death now costs the company two and a half crates' worth instead of just over one. Bringing the dead player's hard hat back to the elevator refunds half of that, not all of it.
The Padded Vest gives less health. Each level adds 25 health instead of 50, so a fully upgraded vest is 175 health instead of 250.
Getting hit is more dangerous. After a monster hits you, it backs off for 4 seconds instead of 8, and it can hit you again after 3 seconds instead of 5.
Staying late gets dangerous sooner. Monsters come back faster the longer you stay on a level. That speed up now peaks after 9 minutes instead of 18, so a long greedy day really costs you.