Challenge 4 is stupid. The AI for Shield is deliberately incompatible with the challenge and the method for controlling the bots is terrible. The control method just barely works for other challenges and the career.
The arrow controls aren't intuitive to me. I'd love to be able to simply click on the tile that I'd like to move to next. That would make it an all mouse game which is just fine by me.
Having the Kongregate logo stay on top is not a good idea for a puzzle. I found no bugs. Don't cover up the instructions. It took me a while to figure out how to flip the pieces.
It seems as if time has a larger impact on the final score than the number of guesses. I would personally think the reward should be much greater for making careful, calculated and fewer guesses.
Keeping high scores would also be a very good improvement.
To pass level 30 you MUST get a large number of bonuses before hand. I suggest concentrating on pool sets (of 9 or more of the same color or symbol) in the early stages to get some good bonuses.
 "Bot Arena 3"){kind=icon}
 "13 Doors"){kind=icon}
 "Jigsaw 2.1"){kind=icon}
 "Hero RPG"){kind=icon}
 "Flash Empires"){kind=icon}
 "Mistermind - Spheres of time"){kind=icon}
 "13 Guardians"){kind=icon}
 "Shumujong (digits mahjong)"){kind=icon}
 "Sling Junior"){kind=icon}
 "P.O.D."){kind=icon}
 "Feudalism"){kind=icon}
 "Ring Pass Not"){kind=icon}
 "Draw-Play 2"){kind=icon}
 "Orbular"){kind=icon}