i'm sure there are some annoying features that were left out of this game, but i can't think of any. rush me through the scrolling at breakneck speeds and force me to guess which way i'll hit an object? not fun.
I believe that a good card game involves challenge over luck. It would be nice if there was a guarantee that it was possible to get the 3 star rating in every round, every time, as long as it is played right.
The only reason the last boss is difficult is because of the lack of pause when moving the mouse outside the game window. That's a pretty lame way to generate difficulty.