This game feels closer to Knytt than to Painajainen, and it feels a bit dull compared to it. Painajainen had some kind of a special feel to it, and that compensated for the monotoneous backgrounds. Kaipuu doesn't seem to have that feel, which is a pity...
Also, I found a bug. When you switch rooms sometimes you can fall through the floor. Try going right (without stopping) in the very first room, and you will probably see it (happens to me every time). Overall, I didn't like the way rooms switch. Even more annoying than in Lilium.
Another (really minor) issue - you can't skip the intro. And I had to restart after I've got stuck inside some platform because of the aforementioned bug. Well, when it gets translated I'll be at least able to figure out how to save and load.
Well, apart from all that - a really enjoyable game. By the way, is it just me, or Kaipuu really takes some stuff from Sean Howard's Negative Space idea? It's all good, regardless.

Uhh...

You can save by pressing down in front of tombstone, and if you get stuck, just press space, it will teleport you to gravestone.

I know it sucks to play game in foreing language.

Yeah, I already figured out how to save. Thanks for that teleporting hint, though.
I found another bug with room transition: when you swim (on the surface) from one screen to another you get an extra "splash!" (completely free of charge) when the room switches.
Also "dark guy"'s wall jump is a bit annoying - I think it simply shouldn't trigger when you're standing on the ground.
Yeah, and now I played enough to figure that it has nothing to do with negative space. A pity, methinks. ^_^

Okay, I finished it. There seems to be another bug, albeit a really minor one. As the white guy you can walk into the vines, and you'll kinda stand on them without falling. You can't climb them, all right (that's for the black guy to do), but you can stand on them.
Also, is it really a good idea for the game to quit after the credits? I wanted to load and see the other ending, and the game just exited. No big deal though.
All in all, I like this game quite a lot.

The game seems to lean heavily towards Seiklus for me, with the whole collecting of little floating fireballs (though I guess these are more like souls? You know, like how they look in japanese floklore?).

It has quite a few of the bugs related to games with unpolished platforming engines, but for the most part it works. It could just be a lot smoother with some polish.

I couldn't tell how to use any new powerups or how either dark or light characters work, since the game was totally in its foreign language. It could benefit from having intructions presented in symbols, like in games like The Ancient's Tome.

It's still fairly decent, but compared to other similar titles it does get boring a bit too quickly. I like the whole snowy particle effect, though.

I only played for fifteen minutes before I became bored.

There's not much I can say in defense of Kaipuu (besides having a much more manageable title than Painajainen) as I think the defensible stuff is likely in the text. I was hoping for something more interesting to be done with the color palette, but rather than being interesting, it just ended up looking bland.

The game has a lot of common, sloppy bugs, some of which x_x has pointed out. There's other basic things too; you sometimes loose momentum when you change screens, making it an enormous pain to progress when a screen scrolls upwards. I also noted slowdown, which for such an unintensive game is pretty poor.

The foreign text acts as an excellent point towards 'How not to design'. This isn't a complicated game, we shouldn't need enormous blocks of text to explain it. Even little titles next to keys and animated characters would make for a significant improvement in clarity without relying on language. Images are more intuitive and universal. (The best example of this in practice, off the top of my head, is probably Mario Vs Donkey Kong)

Similarly, the introduction was quite annoyingly long and unskippable, but moreover, as it's virtually all text, it bears no meaning. There'd be a ton of ways to make it more lively; a little animation, voices or other sfx, even comic panels.

Again, most of my complaints would likely be dismissed or not even thought of if the game was already translated, but it doesn't mean the points aren't valid, english production or otherwise.

Well, the language in question is Finnish (the language of Finland).
And currently if you don't speak/read Finnish, you won't get much out of this game.

The things you collect are souls, because at the start Death asks you to collect them for him in return for your girlfriend.
The colored souls however are your emotions, as to the story, you lost all your emotions, except love and hate/anger, when your girlfriend died.

The white persona is love, and the black persona is hate/anger.
The differend emotions are linked to either love or hate/anger.
Also, everytime you collect a new emotion, you get a description of the emotion.

This setting is because the game was made for the Suomipelit.com summer festival, which had the topic(s) "Love and Hate/Anger".