I need to preface this by saying that I'm impressed at how, after discovering Kraaj for his Gothic horror story and generally gloomy stories, he still manages to write incredibily intertaining funny characters and skits. The comedy in A Rebound from MARS! is great and the MC's snarky personaly is a joy to behold. I think the one joke I'm not a fan of is the one where the MC acknowledges that nametags are a thing: while funny on its own, it didn't really mash with the rest of the humor of this particular story, which is meta but not fourth-wall breaking.
The presentation is top notch, even with the self-imposed visual limitations: the limited color palette gives the game its identity and the game uses silhouettes in interesting ways (OMG that scene with the paw massage, I love it! The length some people will go to get Grange brownie points!). The sound design is also great, not just the music but also the ambience.
If I have to offer some criticism is in the structure of the story. The story is a joy to read, however I do feel that one thing that was missing is focusing a bit earlier on the protagonist's motivation. I couldn't help but be reminded of E.T. and Wall-E while reading this story: the first preoccupation in both of those stories, before we get to the plot eventually leading to the climax, is establishing the seeds of a relationship between the protagonist and his alien friend. In Rebound, instead, the protagonist embarks on a journey right off the gate, and it's only towards the very last leg of said journey that we get to see the two mains establish a connection: everything at the beginning is mostly comedy, busywork, and establishing the characters' backstories (and powers).
SPOILERS to follow
For example, when we get to the bridge crossing, the whole time I couldn't help but think "Why are we risking our life again, instead of finding another way across? What is the urgency, what is the motivation from the MC's point of view?" I do get the answer to that question is probably just "The protagonist needs a project to distract himself from his failed relationship." I just think the story would have been stronger by moving some of the bonding scene from the end to the beginning, in order to make this journey really feel personal.
Also given, the nature of the story, my brain couldn't help but try to poke holes at it at times. The powers of the alien are left a bit mysterious in how they work: the alien will go in the span of the same scene from not knowing what farts or parents are to being able to recount the protagonist's entire life story with very appropriate Earthly terminology. But that's something I can look past!
My final nitpick is that the handling of the "bad guys" left me a bit confused. The reveal is well handled, but I can't help but think it clashes with previous information about the characters (almost like the dev decided half-way through these were going to be bad guys): the way the two bad guys are aware the two protagonists sneaked away during the night but don't seem to react to this information doesn't really seem consistent with the way they are protrayed the following morning. And during the resolution of the story, the protagonist is left in their company, without leaving any clue of what exactly is going to happen to him.
These are all nipicks though: like I said the story was very good!