Some of the Beast cards, at least, aren't balanced the same way the player cards are.
For example, the Ghram Rager costs 1 Momentum for a 1,1 and it has Charge, a powerful ability that is the equivalent of a free turn. To get a refresh, the player needs to spend a card that, from what I've seen costs momentum and penalizes the target card.
There are cards that cost less than their attack and health values in the player deck, such as they might be 4 momentum for a 4,5 or a 5,4 but they usually don't have any abilities. Enforcer seems well balanced at 5 for a 6,6 with an ability that troublesome, AND it can't get onto the table for a couple turns even if the player takes advantage of obstacle benefits.
I did read a tool tip or something that suggested I could discard to improve my momentum but I haven't seen a way to do it.
Ghram Rager would be more balanced if it cost 3 momentum, so that if it is played on the first turn, it's the only play aside from the 0 cost cards. I do understand that the advantage of the Beast suit is low cost, rapid deployment cards the player must keep in check or risk getting overrun by.
On another note, I think the obstacles could be enhanced by providing a form of cover for cards behind them. The game is considering them as under the player's control, if I have a creature behind one it cannot attack it because "only the creature farthest in front may attack." Similar to taunt, obstacles could protect characters behind them from creature and commander attacks, aside from fliers or special commander attacks.
Not sure if that's within the scope of your design, but since the character behind the obstacle cannot attack it, it would be nice for it to provide an advantage.