Some of the stuff you mention is going to be fixed in the next patch, lol
Bowling bulb recharge was reduced a little bit
The level after unlocking Screamelon was completely reworked, and also the night level with multiple scaredy shrooms.
About the art, you can't ask me too much, since all of this is programmer art :B
And I can't add stupidly hard levels in adventure, not even in hard mode (people sometimes complains a lot, although some complains are valid)