DISCLAIMER: My reviews are detailed and hypercritical. This was THAC. You only have 24 hours. It's not easy, and no THAC brickfilm is ever perfect. I know this when I write the detailed review. IF IT COULD BE PERFECT, what could have been added/changed/improved? When we think about all these details in retrospect, we are training ourselves to think about them the next time we make a film.
The animation on this was pretty rough. Set bumps, camera shake, and rather jerky animated motion. That said I liked the use of sloped bricks to create the space creature who helped the astronaut fight the space skeletons. Any time something made a large and quick movement, your timing worked. But walk cycles and slower gentler moves were not a smooth as they probably ought to be. I realize you're probably still learning, so keep practicing!
Your camera angles were all at the "Brickfilm Angle" (Above the character, looking down at them, showing large parts of the set in your shots. I encourage you to research rule-of-thirds, and to experiment with new angles. Try shooting up at your minifigures' faces. It may take a special set-up for the set to get the camera below your subjects, but the result is worth it. Because your film had no voice acting, it relied entirely your visuals to explain the story. I'm not certain what purpose the first shot of your film serves, unless it is to give the main character motivation for revenge.
Which brings me to story. I think your story progression would have been better served by introducing the space creature first. As it stands now, your character is alone until almost the halfway point, when the ally is introduced. Most movies introduce at the beginning, all the characters or at least the presence of a character in the story. And since the space creature is less recognizeable as a character, it's a good idea to clue the audience in on the fact that this brick is a CREATURE and not just a brick. Your interpretation of the theme An Unlikely Alliance was fairly standard and fit the requirements.
Your lighting was consistent and adequate, though perhaps did not communicate mood in any way.
Your strongest aspect in your film was your set. There was a lot of stuff littered around and added visual interest to your shots. Nice sliding door!
Chroma Keying... it's a tricky thing to master, and is not generally advisable for brickfilms (Lego tends to reflect light than absorb it) because the background will shine on parts of the set that you don't want removed. Still, the dark space-sky definitely added to the feeling of the set's appearance. Perhaps, next time think about how you can achieve that look without chroma keying?
All-in-all, keep it up. I'm sure you'll be making excellent brickfilms before too long!