Challenge Card Deck: No endgame cards anymore, but some cards from the UE endgame were moved into the main deck. I think the deck might be a couple cards larger now. The deck has been reworked in ways that you will have to discover on your own, but it now encourages lots of different activities on the pitch.
Challenge Cards: Reworded to reduce word count and for clarity. We removed the requirements to take specific actions to claim a card. No more "If you made a Mark action..." stuff.
Event Cards: There are 12 of them and you can shuffle as many as you want into the deck. This was meant to create a "manage the craziness" option. Event cards activate immediately when they are revealed on the top of the deck. This is where Multiball is now, for instance.
Teams: There are too many things to mention, but the most salient change here was that we purposefully took a look at every team and tried to figure out how to make it more clearly feel like that team. This means that positional players no longer have the exact same skill as one another, for instance. Almost every team got a change in some way, except the perfect team of course ?
Interrupt: Added a keyword to cards and abilities that interrupt the normal flow of play, like Distraction or Frenzy. This should clear up a lot of the timing issues.