It's definetely not a BAD game, just a BAD entry on a SUPERB franchise. Though judging it to all other videogames, I still find it good.
My childhood was full of Brawl matches, and was my first fighting game. I'm actually not a fan of the fighting genre, but Smash's dynamic platforming and simplified mechanics were a good entry point.
But, it definetely has bad poitns, such as its slow feeling, lack of some fanfavorite characters, and the presence of other ''casual'' mechanics that are too much (tripping, anyone?). Anyhow, the OST is amazing and side content is plentyful.
Finally, hot take, but the Subspace Emissery was, IMO, a really good attempt at a story mode, and the best parts were the cinematics and interaction between characters. Though, it lacked an interesting premise and memorable stages.