I'm having trouble figuring out exactly what it is, but this film is severely lacking in something the first one mastered.
Let's start with the easy stuff. There are way too many references and bad puns. Some reviewers would call these references "jokes the adults can understand", and while that is true, they aren't funny. They're just kind of there. They are references that exist for you to say "I get that". There is no "ha" preceding that. Yes, the original also had references and bad puns, but they were used well and there weren't nearly as many.
The first LEGO movie was very self aware, but it had a soul that really seemed to care about what it was saying. The second LEGO movie was so self aware that it was very difficult to take seriously.
There was an obvious message about how growing up should be about learning to work with different people, but it kind of fell flat beneath the veil of "play with others even if you don't like how they play". It honestly made me a little angry. Maybe it wasn't intentional, but the film seemed to suggest that traditionally masculine things are incapable of being imaginative. I couldn't help but feel a pinch of modern social politics biting for my throat.
The first film felt very apolitical, and I believe that's fitting for a film about a franchise of toys that cradled our imaginations before we cared about politics. This film certainly didn't "ruin my childhood" by any means, but it was a disappointment.