Let's take something really simple that I don't believe was ever addressed: What was the original mission here? Where was this Turnip with all these people going? Were they just exploring alien worlds? The movie seems completely uninterested in sharing what these characters motivations were for even STARTING this journey.
And the rookie at the start of the movie? The one the movie says BUZZ should care about? Yeah...gone, never shows up in the rest of the movie. The MOVIE doesn't even care about this guy enough to focus on him, WHY SHOULD WE?! They could have just made him the future-Commander later on, to give him a reason to dislike Buzz, but NOPE!
And NO ONE comes looking for them? After DECADES? Were they not in communication with Earth? Were they not supposed to send reports back to Earth at different points to report on these alien worlds? Are there NO OTHER spaceships out there also exploring OTHER corners of the galaxy they could contact for assistance, somehow? If Star Command doesn't exist yet, then FINE, but SOMEONE on Earth should have noticed they were missing, unless Earth is destroyed in this universe.
And then there's the planet itself. It's BORING. No alien ruins, no interesting monsters, NO NOTHING! There's nothing on this planet to make the audience interested in staying here. Why does a ship full of explorers and scientists WANT to stay on such a boring planet? Are they studying something?
There are the alien vines that keep dragging people away....which is played off as a joke and gets forgotten about halfway through the movie. Originally, I thought maybe the planet was sentient or something and trying to WARN the crew about a disaster about to happen. But...nope. We learn nothing about the vines. They could have been cut out of the movie entirely and we would lose NOTHING!
Same thing goes for Airman Diaz. Do you remember Airman Diaz? Short pudgy mechanic guy who kept getting grabbed by the vines? WHY WAS HE IN THIS MOVIE? This character was pointless. Buzz doesn't even mourn his death.
And...why can't they just repair the main ship? They have the resources to make DOZENS of prototype starships. And nearly UNLIMITED amounts of fuel, not only enough to make a bunch of new fuels for the prototypes but to power their base and cars and weapons.
How is it that a bunch of scientists and explorers have never HEARD of the concept of time dilation? And why didn't it seem to affect the Big Ship? Did they have...paradox absorbers on the Turnip? This could have been SO EASILY solved by just having the explanation take place BEFORE they built the first prototype. But, they wanted a dramatic reveal, so the world-building suffered.
And these ship designs are completely wasted on this movie. These are cool ships. But, the movie is MUCH more interested in the FUEL instead of the SHIPS. We aren't even given any reasons why these ships are better than the old ones. We can ASSUME they made small, incremental improvements...but we have NO IDEA what they ARE. And all of them having the same color scheme means they all blend together during the movie. I could see some people not even noticing they were different ships.
And...the fuel...couldn't they have tested if the fuel worked on the planet BEFORE sending Buzz out on a ship? Wasn't there some way to test the fuel mixture so they wouldn't have to wait YEARS to see if it worked? Couldn't have they used it on one of their cars or just tested it in a lab first? Just...set it on fire and see if it actually BURNS before putting in a spaceship, maybe?
And...couldn't they have sent a hyperspace MESSAGE back to Earth instead of a whole spaceship? I feel like it would have taken less energy to send a radio transmission instead of a spaceship via hyperspace. But...I guess they can't communicate with Earth..."Because the script says so"! But, at least they could have tried a few different plans at the same time, instead of putting ALL their eggs in one basket. But, NOPE! These are the least experimental and curious scientists in movie history!
They had the resources to make full-on test-tube babies onboard this ship? And they way it's presented, it's not somebody donating some sperm, this is probably supposed to be a mixture of the two ladies. They had near cloning capabilities onboard this ship? And it still works FINE after the crash? THIS is the ONE thing the scientists aboard the Turnip succeed at?!
The movie makes a big point about everyone accepting just living on this planet forever. They've made FAMILIES here. So...did NO ONE on this ship have loved ones on Earth? Did no leave behind wives, or children, or siblings, or parents, or friends, or ANYONE they cared about seeing again on Earth? What about those guys? Or was this a suicide mission from the start? Yes, fine, it's sad that some kids won't be born in this new timeline...but it's also sad that none of the people on Earth will ever know what happened to their loved ones on this ship!
And...that's another thing. Would changing the past OVERWRITE this timeline or would it just create a SPLINTER timeline? The movie never brings up the possibility. I'm willing to accept these time travel rules only allow overwriting...but this seems to be new territory for EVERYONE. I don't think anyone actually KNOWS what the rules are. So they literally could have had it both ways! The people in this timeline could have survived AND everyone gets to meet up with their families back on Earth! But, no! "Because the script says so"!
A entire team of scientists working DECADES can't solve the fuel chemistry for hyperspace travel...but a "toy" cat can? How incompetent ARE these scientists?!
And...the future-Commander's motivation for stopping the tests seems pretty weak. They don't seem to be running low on resources. It seemed like they were setting him up to be going mad with power...but they don't go there. If he had been someone Buzz had insulted back when he was a kid, it'd at least be for some personal motivation. But, he just stops it because..."The script says so". It just comes out of nowhere and doesn't really add much to the movie, except getting Buzz to be on the run. We're given VERY little information about why the future-Commander does the things he does.
The reverse-sandwiches are stupid. It's a joke, but its too goofy of a joke for this movie. It doesn't work in this setting. Arguably, it causes too much tonal whiplash.
Same goes for the confetti.
The room everyone gets stuck in so they all have to work together could ONLY exist in a video game. Leaving the power source for your lockdown in the same room that's being locked-down makes no sense. Again, it's because "The script says so"
And SO MUCH of this film's pacing feels slow and talky...just to BE slow and talky. We spends several scenes watching characters EAT or long, slow establishing shots of the view. It's just feels padded.
Oh, and as for this movie being "character-centric"...no...no, it really isn't. BUZZ gets focus and development, sure ...but NONE of the OTHER characters do. Everyone just..goes along with everything that happens. No one else has their own goals, or motivations, or ideas, or anything. They leave a character behind as a joke! And they're all so bland! In a movie all about how we should care about people more than the mission...they spend 80% of their time on the mission. They didn't make us care about these characters. Even some of the likable character like Buzz's friend and her daughter were kind of forgettable and bland, and I chalk up their entire likability to the performances of the actors. Why should we, the audience, care if they get erased?
And even Buzz's development is...really cliche. "Care about other people...or ELSE!". Even his reason for keeping others at a distance feels over-safe and bland, being a screw up in the past. And we don't even get a flashback to SEE it, it's all done through dialogue. It's unsatisfying.
And probably the biggest complaint about the movie...where did the ship full of alien robots come from? This was most likely a sequel hook...but if so it was teased VERY poorly. We are given NO CLUES about where this came from or what it means. Was it made by the crew on the planet? And it's just WAY too big of a script convenience the way it's presented. "Oh, here's a army of robots you can use that obey your every command!" Maybe a sequel would have redeemed it, but it's VERY unsatisfying in this movie.
What did future-Buzz EAT onboard the alien robot spaceship for decades, anyway? This is nitpick, but meh.