As a sci-fi fan, I found the film mildly entertaining, if only for the setting and concepts, but I get why it didn't land well with the general audience. I think the film had two major flaws that dragged it down.
First would be that the film couldn't decide what it wanted to be. It took itself too seriously and had too many convoluted concepts (time dilation, time travel, alternate timelines) to be enjoyed by children, but it also didn't really explore any of it's themes or concepts well enough to be enjoyed by adults. This whole film really comes across as Interstellar-lite, which is just an odd thing to base a kids film on.
The other issue for me was the characters. They just weren't very engaging. Buzz himself came off as kind of humorless and dour, and the rest of the cast was entirely one note. Buzz's team in particularly just felt tacked on and didn't really add anything to the film. Tim Allen is a better Buzz Lightyear. Even Patrick Warburton is probably a better Buzz in terms of being engaging and fun. Chris Evans does a solid job here, and I kind of agree that he brings a more "human" quality compared to the wacky Tim Allen. But when you look at how devoid of energy the film is, I have to wonder if Tim Allen could have somehow injected some life into this movie with clever ad-libs. This movie needed energy, and it has nothing in the tank.
Ultimately, I think the film just needed to pick a lane. Either make this a fun adventure romp across the galaxy, or lean into the mature themes and ideas. As is, it's a film that didn't really make me laugh or make me feel anything, it's just kind of "there".
