Hello! Welcome to Feedback Quest 5!
Oh how I waited for this. OH HOW I WAITED! I was anticipating a lot of good things, and wow was I blown out of the water for what's happened since FQ4. New maps, new enemies, a better scaling metal bonus. It was to be an exciting time! And it was! Mostly.
One of the new enemies, the Cart, may have a tuning issue as waves get higher. As the stages went on, I found Carts went from fairly easy to impossible. By the fifth stage, carts reached a point where it wasn't conceivable that they could be beaten. This was even with me switching tactics. When I got the two cart wave, it was just too impossible to deal with. I could barely keep my turrets up to even hurt them, and the existence of two on different paths meant my damage would barely overlap between them.
I don't think the problem is a big one, either. I think it's just the health scaling per wave you have going on. It's likely just slightly too high (by a couple %) when it comes to increasing HP.
Other than that, I don't have much feedback to give. I still feel the knife block needs to be improved (In fact, I feel like the knife block should be the key to taking out carts. That would be a great design that ensures people use them along with other turrets).
I can't wait to see the next leap in improvements!