While this game was very lacking during launch, by this point it has received several updates and it's quite good.
Characters were / are planned to be added, totaling the roster to 25 characters. Granted, it isn't that *that* much, but the diverse amount cartoons make it better. I mean hey there's only 3 SpongeBob characters so there's a lot of variety. The voice acting is also very, very good. There's just something different with cartoon characters talking. It's nostalgic.
Music kind of sucks. Remixes of cartoon tracks or just straight up the tracks themselves directly from the show would have been ideal, but a lot of the music is random, mediocre tunes. Definitely its worst quality asides from the next point.
Visuals are meh. Characters could look a bit better. Take Patrick for instance. He just looks like a pink blob with big eyebrows and a hole for its mouth. Most are fine, though.
I'm not really reliable for the core fighting mechanics as I'm not really into competitive and only bought this for the SpongeBob stuff, but it's so fast, wild and fun. Moves are happening left and right endlessly and matches can get very hectic, all for the better. Items are also a fun addition that made the already fun gameplay even more fun. Very good gameplay in my opinion.
Final standalone complaints: it takes so long to load. Whether it's online or a regular match against a CPU, you have to wait quite a while. Now I'm not sure if it's just my opponent causing it during online, but it's definitely the game's fault for taking so long for the regular CPU match. It gets quite annoying. The volume could also be lowered a bit. I have my Switch at normal volume and am fine until I load the game and lose my eardrums when the announcer yells "NICKELODEON ALL STAR BRAWL!!!". I want to keep my ears, man...
Overall, while it might be quite lacking in the artistic side of things like music and visuals and there's definitely some nitpicks here and there, the game is still pretty good in all other categories, resulting in a pretty good game. At the very least, it's definitely undeserving of all the hate and "30 players" memes at this point. It's improved, give it a second shot.