So I've played the game and I will just go through my thoughts quickly.
First off, the art is very impressive, pretty professional looking infact and I really enjoyed the style. If anything, it could have used a few more effects, but it works very well still, giving a scary but sort of cute look. The music also fits the game quite nicely and is very well made.
As for the gameplay though, it is quite repetitive with no real progression. The obstacles all behave pretty much the same, just with different sprites. I found the collisions to also be relatively counter-intuitive, as a visual touch between them and the player is not actually neccessary to lose lives. Furthermore, everything moves somewhat slowly which makes the jumps harder yet. I believe though that if you were to add varying jump heights depending on how long the space bar is held, or a slide on the ground, for instance, the gameplay would have a lot of potential. I really enjoy this kind of minimalistic gameplay when used to full effect, though in its current state it is still very monotone.
I feel that the same applies for a lot of the game's aspects; the title is not really implemented, though the phrase "Within" carries massive potential for anything horror-related. I think that just expanding on the concepts present could make a really nice game, but in its current state it merely shows some cool visuals and concepts.
Something else I liked though is the site itself, (aside from a grammatical error "Are you courage enough"), as the description is well written, especially with the effective use of bold font and capitalization all the while it is kept short and sweet.
I definetely would love to see the concepts explored further and hope that you found this useful.
Sincerely,
Gefüllte Taubenbrust from Mandelbrot Studios