So I just played a bit of a solo campaign and here are my impressions:
the character creation process is as freeform as it can possibly be, which I wasn't that used to but it was fun. However, there is the restriction of PCs being part of an elite and top-secret group of explorers. I think that if you're gonna put restrictions on characters (which is totally fine btw), you should provide some creative impulses for players to work with, i.e. what makes those elites roughly the elites that they are.
With other people, this might be different but solo just feels too stagnant for me. While I can, and did, tie different debriefs together (esp. when I rolled the same planet again), the pace at which this story developed was too slow. More importantly, because the only tracker towards progress is the Dial Home gauge, I didn't feel like I was working towards some narrative goal within the parameters of the game's design.
A jam-specific criticism I have is the usage of the d6 for planet designations. There are three dice rolls used in this game, and one of them is not one of the Lesser Love Dice, when it feels like it could have been incorporated fairly easily. But I'll gladly read through your throughts of using a d6 and not a d4 or d8 :)
Overall though, I did have fun with the journaling aspect of I Went Through the Stargate Once. The prompts are fun to work with. It is just on a broader scope, where I think it could have used a bit more work.