Endless mode would be nice. Right now, its very very hard to get away from the starter deck. You basically spend most all of your time playing with the same starter deck followers. There are other cards out there for you to discover, but since they rarely ever show up, the game will be finished before you can actually get totally away from your starter deck. (can never escape the starter leader cards) Then you start a new game, and your deck is again the same.
I sometimes still cheat myself into levels 3 and 4 (sorry), just so I get to play longer. The longer you play, the more you can really customize. Some of my late game decks were really fun, because they were totally different than the starter deck.
Of course the new starter class will also make the early game fun again. But an endless mode would help too. Even if it just gives you Pit Nine for every milestone.