You really pulled off the classic Space Serial feel, with the music and the tone. Even the sets are designed in the style of those old sci-fi films. This is a really creative film, and I think you succeeded in what you wanted to accomplish pretty well. I have not seen any of the previous episodes in the series, but I'll definitely check them out.
I really like your use of practical effects, especially the lightning effect near the end, and the animation was good.
The shot at 1:55 felt a little too long for me, but I'm not sure if that might not have actually been intentional, as a lot of old films in the style that you are replicating did tend to have long shots like that.
Spoiler (click to read)
Also I really love how easily they took down the martian, by simply tapping on his head
As I stated earlier, I really like your set design. My only critique on the sets is when they're on the mine cart thing, and you only rearrange a couple of bricks to convey that it's another shot. I feel like maybe you could have done with changing the set up a bit, just to make it a little clear, or perhaps moving the position of the camera.
Overall, though, this is great. I really enjoyed it. It's a great homage to the old classic sci-fi movies!