Where's the safety inspector?! Who allowed this library to get built? :P
Not bad, but there are a few issues that kinda take away from the fun factor.
-The biggest issue is that the jump button doesn't work all of the time. I'll try to jump to the last platform of the second area, I hear the jump sound effect, but then I fall straight into to the abyss.
Same thing happens when I try jumping on the spot. Most of the time it works, but it won't just often enough to cause a pitfall. Since I've no experience in Construct, I don't know how the programming works. However, I can mention the details that cause non-jumps to occur.
-Whenever the character tries to jump from a quick pivot to another direction.
-When trying to jump off a platform moving up and down.
-When trying to jump while running on a platform
-The game is a little bit empty in the sound department, which sort of hurts the atmosphere of the game a little bit. If you wanted there to be no music to help the player focus, then you could add some sound effects to help give the player useful context. Such as...
-A sound effect for a restart back at the beginning, 'cuz BOY did I die a lot. :P
-A sound effect for the fireballs, as they almost blindsided me each time. Just something to act as a 'HEY THINK FAST!', y'know? haha
-Unique sounds for falling or landing on spikes. Something to let you know you made a mistake. Nothing loud of course, as that'd get obnoxious after playing too much.
-Another problem is that I walked into a wall after getting through a section, and then immediately died and restarted. I'm assumed that there might have been a trap that was GOING to come after me, but it hadn't come out of the wall nor was there any indication that something was there. The reason I went to check the wall was because in previous sections I had to go through a fake/hidden corridor to flip a switch, so I felt kinda ripped off.
I know now that there was a fireball that was going to come out, but it should only have killed me if it was launched. A way to fix this would be to have it spawn after reaching the middle of the corridor, as opposed to just coming out of hiding from the wall.
Just make sure you can smooth out the controls to prevent faultless deaths. Those kinds of deaths are especially frustrating in a platforming game where control is the focus of the game.
Best of luck! : D