Completed the game yesterday. The second to last boss, King Dice, took a lot of time. I could get to the last phase many times but I had problems with the cards he dealt. I also sucked at the dice game and hit a lot of the fields.
The Devil went down shortly afterwards, he wasn't too hard. Ended the game with a 96 % completion, missed some coins on the Run n Gun levels.
Apart from the relatively long loading times, I think this game was marvelous. It was never really frustrating as it was mainly down to skill and choice of weapon. Some levels were very hard but overall, they were balanced really well.
And the presentation, truly outstanding.