Rather "meh"
First, I'll start with the preloader. The blood splatters and copious amounts of red just make it really cluttered and ugly.
The background in the animation has a kind of cool, bleak style to it that the characters do not. They look rather lousy and are barely animated; just tweening along. The music accompanying them was a good choice though.
Not to spoil anything, but the screamer at the end sucks. It sounds like you just yelled into your microphone and spiked the mic. Also, the accompanying image of "It" is not the most terrifying thing you could find either. The flash as a whole would be better without the lame screamer at the end.
All in all, a fairly competent effort marred by a screamer and some iffy art. Keep trying, your skills can only improve.