Here are a few problems I found:
1. the I and the L are very confusing, maybe use the lowercase i instead.
2. when playing the hardest level, the sheep getting tossed into the air makes the other letters on the other sheep hard to read.
3. There are times on the hard level that it's impossible to type the letters; not enough time between when they jump and when the letter is generated. My sheep were jumping before the letter would generate.
Other than that, I enjoyed it very much.