I occasionally see people debating this and I can't help but feel- Isn't Across the 2nd Dimension like- Objectively better than Candace Against the Universe in nearly ever capacity?
Don't get me wrong, Candace Against the Universe isn't bad and I'm sure there are SOME aspects of it that are better than Across the 2nd Dimension, and Candace Against the Universe was great to see as it was ultimately a return of Phineas and Ferb out of Nowhere.
But Candace Against the Universe seems to just be a glorified regular Episode. It follows the same story beats as a regular Episode and heck- Even the concept of Candace deciding against busting her brothers isn't something new (I think Phineas's Birthday Episode is a good example).
In Candace Against the Universe, it's even teased at the beginning than Perry cannot let anyone find out his secret identity. This doesn't really come into play again as Perry is just as steaethy as always and having them find out his secret identity would just be too similar to Across the 2nd Dimension... But that's it.
Across the 2nd Dimension takes the concept of a regular episode and flips it on its head, having Perry's identity revealed and genuine drama leak out of that. The Finale with all of the inventions being used at once, along with Candace going to get Linda as if that would do anything, is a great climatic Finale. Heck, this Movie could easily be the Finale to Phineas and Ferb.
I think the only way another Movie could reach this height again would be... I dunno. Have Linda finally see Candace was right the whole time during a cinematic voyage where she can't exactly: 'bust,' them at the time. Maybe Candace finds out about the Mysterious Force and and in the end, Linda realizes Phineas and Ferb are needed to save the universe of whatever and Candace learns to accept her brothers and what they build.
But even That would be retreads of previous Episodes. Across the 2nd Dimension- Having Phineas and Ferb find out about Perry's identity, was something that had Never been done before in any Previous Episode.