Alright, so here's my two cents on the update.
Firstoff, let me say that the boss and the zombies are great additions to the game. The boss is hard to beat, which in turn makes it a challenge and actually makes it feel all the more satisfying when you beat him. Zombies are cool as well, though I wish they weren't just a reskin of the robots. Wave 666 seems cool, although I havent played it personally.
Second, the items. The whole idea of potions is great, but the problem is they expire. Why cant I have flaming footsteps year-round Valve?! In any case, you also have what they did before Meet the Pyro if I am correct, in that you take a certain amount of items and craft them together. Apparently you take 7 cursed items and craft God-knows-what. Hopefully something permanent.
Third, the eerie crates and keys. A great way for community contributors to get their items out there, and for Valve to troll us all and make even more money.
Overall, a solid 8.5/10 on this update for me.
*Also - WHERE IS MY HALLOWEEN COSTUME DROPS. I WANT TO CATCH EM ALL!