As you get faster, it is harder and harder to move left. Once your speed reaches a certain level (~70) you are no longer able to move to the left at all.
Fix your game so that you don't find yourself stuck in a corner at tier 21 trying to move the opposite direction while a rolling circle kills you. The directions stick at least 2-3 times each tier.
On level 9 it is almost impossible to see how much cheese you have because the numbers are the same color as the background. Might be a good idea to put a static background behind the cheese counter.
Although the game is extremely difficult, the last 2 bosses were designed well and almost made the hair-pulling difficulty of the previous 5 levels worth it.
 "Loot Hero"){kind=icon}
 "BoomsticK"){kind=icon}
 "Defend Your Cheese"){kind=icon}
 "The Last Defense"){kind=icon}