Indie mash-up!
Well, it seems nobody noticed, but the gameplay is ripped straight off of "Knytt Stories". It's an indie game that plays not only exactly like this, but if has its own level (Or "Story") editor.
As for Insidia, I'll give it an 8 because it stands alone as a sort of experience (It's very similar to the Xbox Live Arcade game Limbo). Although again, there's no gameplay change from Knytt Stories at all except the decrease (That's right, decrease) in the amount of power-ups (Besides, I love, love, love that ghost upgrade).
I'd have given this a higher score if it'd expanded on the gameplay of Knytt Stories (and thus been longer), but the score could've been a lot worse.
I like the choice to make this a flash game. It's a much, much, MUCH better way to be heard than to make a Knytt level nobody's gonna play. Then there's atmosphere. It what's getting this game all the talk. And there's not much to say about the atmosphere that can't be said about Limbo, except that Insidia is a little more subtle about things. There's a feeling of innocence in the world that quickly turns more intense when the screen is switched. Excellent use of screen switching.
Gameplay-wise it's nothing new, and atmosphere-wise it's again nothing new. But the unoriginality really doesn't take away from the fun because you managed to take an obscured game's gameplay and a slightly overpriced cult game's atmosphere and give then the attention they damn well deserve (Knytt Stories more than Limbo though).
As for the multiple endings, I think it's a nice little thing to keep the player a little more lively while searching for stuff.
As for anyone who wants more of the gameplay, check out Knytt Stories (And make a story while you're at it), and for those who love the atmosphere, check out Limbo on Xbox Live Arcade.