Nice job! The animation was fairly good, could have used some improvement but wasn't that bad. There was also a little bit of light flicker throughout, but it didn't really detract from the overall film at all, and it wasn't very noticeable.
One thing I really liked was the part where the instructor is showing the students (is that what you want to call them? ) how to build the tree - don't ask me why, but it caught my eye. Also your design for the blue mailbox - simple, but extremely easy to identify. Love it.
The one thing that bothered me the most throughout the film was the changing of the white mime heads to yellow heads. I'm assuming this is a result of a fairly limited supply of minifig heads, and I can completely understand it, but I would recommend buying some faces with different expressions on them from Bricklink or somewhere so it won't look strange.

Great film overall, you told the story well without any use of dialogue. Again, nice job.