I only played it for Raging Flame Sprite and the gems. But aside from that, I agree with you. They should have at least had more variety with the monster opponents and not just the same ones over and over. And the BGM nearly put me to sleep.
If those changes include some upbeat music and letting us choose what rewards we want in the shop instead of it being randomly selected, then it could be more enjoyable, depending on what cards they have.