Veteran and Nightmare difficulties definitely need to be scaled way back unless they're going to add another difficulty inbetween Survivor and Veteran.
The cards are definitely an interesting addition once you get used to them, though I wish the characters were more different.
I like the special ridden having weak spots, but I feel like the Tallboys have way too much health for how fast and hard to avoid they are. Should pull one of those three things back: health, speed, or reach.
The guns feel better and better the more you play with them.
I like the ability to make strong melee builds
I like how it punishes you more for making mistakes than L4D did, barring L4D's expert mode (but I still wish B4B's difficulty was lowered at least on Veteran)
Definitely need to be able to swap attachments on guns
This game would be worth full price if they had 5 campaigns.
It's fun with friends and will probably be worth the money after a slight discount or DLC gets released.
I didn't touch the PVP and don't care to.
Overall, I liked it, but I see a fuckton of ways that it could be much better.