Regarding new infected:

The only new infected we saw in the level we played was the Charger.

He looks sort of like a mini-tank; he rushes at you at the ground level, super fast, and knocks you back and onto your ass, dazing you for a moment while you shake your head and get up. It's not as incapacitating as a smoker or hunter, but it takes you out of the fight for a moment, which can cause a clusterfuck. After he charges you and knocks you out, he goes for someone else.

Lynx and Scotty got boomed. I didn't actually see a boomer, so they might be able to offer more insight. The hunter, smoker, and tank seemed exactly the same (the tank seemed a bit easier? But maybe we were on easy mode, I can't be sure)