52 is not "panned", it literally says on Metacritic that it indicates mixed reviews

Plus it got a Grammy nomination for Album of the Year.
As for why people on ATRL consider it to be a good pop album when critics might generally disagree, I think that the album does a really good job at being exactly what it is. Its just a good pop album with great melodies, a good production, and relatable lyrics. It never tries to be anything that its not and it also has a really good theme that makes a lot of people feel nostalgic and reminds them of when they were a teenager. Its just an album to make you feel good but to be fair there isn't really much artistic value on the album, but thats not what the album is trying to have.