Since boxes can fall of an edge, you'd expect the game to have physics where you could sort of use a momentum-based fling to throw the boxes to the other side. You'd also expect the text to not be blurry, but whatever.
First memory leak I could find was in level 3. I played levels 1 and 2 over and over and every now and then one would occur. I know it's a memory leak because it will increase memory usage for a level and continue to rise even after the level closes.
I think the gold payout is pretty slow. It kinda makes the whole game drag. It'd be easy enough to just double the current amount of gold and then it'd be a bit more acceptable. I think the differences in prices are fine (like a slave partner is about 5x as expensive as a cheap piece of armor), but it's very difficult to get armor in the first place. You have to do like 3-4 difficult and/or long fights just to get 1 piece of cheap armor.
I easily have to agree with any comment about gold being the main deal here (you can have a heavy iron or heavy crystal deck and still only need 2 or 3 max of each of the respective cards, but you need LOTS of gold; you need +21 or more to easily win, although wins are feasible around +15). I also agree with the UI issues. I'd like to add one more in that I think there should be a % of all cards somewhere. We should know if it's worth it to keep buying rare and legendary packs or if we're missing basic cards or realistically, we should know how many cards there are total. This game is so fun, but there really are some major overlooked things. I think you could be one of the few game makers to bring another excellent game to Kongregate (Cardian) if you'd take everyone's advice (not even just the top 5, 2000+ comments).