I liked it.
Kinda had a problem with jumping at first and at a few times (no complaints about jumping while holding a box, that was completely the point to not be able to jump as high).
My biggest problem was that for whatever reason, the right side of the screen couldn't be seen. Maybe the flash window (or something) was shifted a bit, maybe my system downloaded it wrong (or something). This made some levels a bit trickier or more misleading than required. However, I was able to complete the game without needing the walkthrough so I didn't take points off from that. Though it did make one level a bit annoying with having to guess there was a box offscreen and later a teleporter.
Only level I didn't like, though I'll admit it was clever was the level with the teleporting boxes you had to hop onto.