Wolfox

It wasn't just the tripping, the slowed gameplay, and removal of techniques.  It was horrendously balanced, physics were terrible and allowed people to manipulate the game in really dumb ways, and discussing the game was hella toxic.  The game was developed in a way that was messy and made no sense.  Part of the reason why the game was a mess is because it was being developed with a casual audience in mind.  And certain elements were made so that little kids wouldn't feel bad if they lost to a higher level player.  Unfortunately when it came to higher level play it made it so that skillful players could manipulate those physics made for casual players in ways that made the game really lame. 
My issue with brawl isn't what it was like competitively, but how it functioned as a smash game.  I grew up playing every smash game and loving smash, but when I got older and started to get used to brawl and how it functioned, it made me realize that I hated how that game felt and almost made me give up on smash entirely.  Smash 4 fixed that problem for me.  A lot of the issues I had with Melee and Brawl were mostly fixed in Smash 4 and now I am happy to play smash.  Ultimate only made things better for the most part.

I was one of the few that didn't want subspace to come back simply because when I play smash, I intend to play it for years and years.  Most people who want subspace intend to play it once, shelf it, and play it once in a blue moon.  I rather have the devs take the time to make the core gameplay as fantastic as humanly possible rather then try really hard to make a half assed game and one big piece of single player content.  That is my issue with NetherRealm games.  Main Game sucks, but their story modes is what makes them the most bank.  If I wanted to play a game for the story, I rather play a game that is focused on the single player content like Zelda or Uncharted.  Fighting games are not developed for single player, and I rather have the multiplayer be as strong as it can be and replayable as it can be, rather then have another mess like what Brawl was or what NetherRealm games are.

while all these regards are to smash as a fighting game, that's not all it is. Brawl in particular, smash is also a party game. one to turn on and play with friends and just have fun with. 

When I say balance, I don't always mean competitive viability.  The game isn't fun when the characters aren't acting like how they should.  It's hard to have fun when the game is fundamentally flawed in all the worse ways.