Skip the cut scenes and you have an enjoyable game!
The difficulty was ok for me. I'm not the best player in the world and I was glad that I could grind lives in the easier levels to prepare for the harder ones. Some were complaining about the patrolling AI but that's totally fine in this genre I think.
The only truly bad part of the game are the cut-scenes. The story is bad and extremely stereotypical. The models of the side characters are very rough and ugly and the whole style is made for three-year olds. Everyone is speaking really slow and the voice acting in the German version is probably the worst I have ever heard. Fortunately you can skip the scenes. Don't worry - you'll miss nothing.
So if you like platformers and don't mind spending a lot of money on 5 hours of gameplay (+ some time for collecting stuff and the bonus levels maybe) I can recommend Klonoa to you.