Maybe it's just me, but I'm detecting a certain annoying pattern here.
I have a couple of level 4-5 cards, and a small bunch of each of the level 2-3 cards.
Playing against Bored Guardsman and Wandering Trickster doesn't really seem to alter this spread.
Playing against Drunken Cardsharp feels like I have more to lose than to gain, because he can whip out one of those level 10 specials that can't be defeated which then ends up blocking the field, and apparently gives bonuses to the rest of his moves, or something like that (I have no idea what's going on there, but sometimes it's like having one of those leprechaun cards on the table is an instant loss). I can only win engagements against him by playing for cards. In other words, aim not to win, but to flip the best cards I can, so that I'll lose most of mine, and maybe gain one or two of his. And that feels really random, and fatalistic (if that's a word I can use for a card game).
Edit: and when I say here 'win engagements' I mean: have better cards after winning, instead of having worse cards after winning.
Playing against anyone above that feels like a steep uphill battle when most of the cards they field are higher level than me.
In other words, there doesn't seem to be a mid-level opponent there. It's either low level, random blasts of undefeatable cards, or too high level.
(Also, I really hate not being able to pick my initial hand in the higher level matches. I wish there was a way to allow that without it breaking the card collection system.)
I've only played 146 matches (which I'd argue is really low for the game), so I don't yet know how accurate this is.