I enjoyed this. (I'm a fan of the speed champions series, so you have a +1 to likeability from me).
I really liked your set design (lots of varied space and detail), and the concept was fresh. I was really interested in the close-up chase view as the minifigure walked through the facility, it's not something you see often, and I've been working on coming up with a reliable way to do that myself.
Out of curiosity, what type of camera did you use to shoot the close-up follow view behind the minifigure?
It was also fun to watch the Lego wheels put to the test.
Your sound design was okay. Volume leveling would have been nice, that alarm was a bit too loud. Also some more time put into visual storytelling would have made the fact that the operators were playing a joke on the janitor a bit more clear.
The first time I watched it I was too bothered by the very loud alarm to get that the janitor was being pranked. The noise drew too much attention to itself.
My main suggestion is working on your frame rate. Take more pictures, and practice "easing-in and easing-out" to really clean up the movements. It takes a lot of practice, but the end result is worth it.
Overall, pretty well done for your first brickfilm!
I imagine you at least have some experience and/or knowledge with film/video prior to working on this. It shows!