Possibly one of my weirder takes, but an element I've grown to really like about the first Super Smash Bros. is that - due to the limitations of the N64 sound hardware and the decision to make almost every piece of music in the game a remix - it really feels like the game has its own more unified musical identity in which every "world" fits, rather than just being a collation of different "worlds" into its own through the use of gamerips.
There's probably a ton of reasons why Smash seems to have... lost a little identity over the years, but I think that's a small part of it. Also, Melee's orchestral tracks are fantastic (and I won't deny that in the slightest), but I do think there's a certain... appeal to the first game's sound. Not sure how to put it.
making series with odd numbers of characters stick out even more.