I rented it a few days ago. My only previous experience with Klonoa came from the GBA game Empire of Dreams, which I unfortunately never finished. I might have to find a ROM of it and actually beat it, though, because I thoroughly enjoyed this game.
The voice acting was sort of a weird experience for me. At first I was extremely skeptical of the English voice acting because I was so used to the original "Wahoo!" But after playing through the game with the voice acting on English, I found it to be acceptable. I'm still not entirely sold on Klonoa's English voice, though- while it gets the job done, it doesn't seem like it fits the character all that well. It's a little too Sonic the Hedgehog for my tastes. On the other hand, the Phantomile voice track takes a bit of getting used to if only because of how bizarre it is, but it fits the whimsy of the world and has the Klonoa voice I know and love.
It's not a very difficult game, save for a few moments in the last few levels that required a bit of careful platforming, but after finishing the main story there are several unlockables that add some much-needed challenge. The final unlockable vision is
ridiculously difficult when compared to the rest of the game. I'm not sure if it's possible to finish it without going through most of your lives- it's a good thing they practically throw them at you in that level! I haven't tried the Mirror Mode at all, and I probably won't be able to since I need to return the game today, but I'd imagine playing through the levels backwards can be pretty difficult.
The ending caught me by surprise. I knew that it was going to be fairly emotional because of a few mentions Nintendo Power made to it a while back, but that didn't keep me from being surprised.
It was rather surprising to find out Hewpoe was essentially manipulating Klonoa from the start. Even though his intentions were good, he was still using Klonoa for his own purposes. I think that's what made the ending particularly poignant: Even though Hewpoe just told Klonoa that everything he knows is a lie and that he doesn't even belong there, he still wants to stay because he still feels like he really does belong there. It's kind of similar to Pokemon Mystery Dungeon in that aspect... but at the same time, not exactly.
All in all I found it fantastic! If you aren't sure about Klonoa, it would be a great idea to try renting it, since you could probably beat it thoroughly over the rental period. I'm hoping that the second game in the series will also get the Wiimake treatment, but considering that Klonoa has never really done all that well in the U.S. that doesn't seem very likely... I can at least borrow Klonoa 2 from a friend of mine who has the game, though, so it's all good!