If the initial reveal for Pichu was positive, I suspect the first time playing was a horrible surprise.
Wasn't that big of a deal, people played characters they liked, not because of stats or tiers.
Competitive online scene didn't exist.
The competitive scene that did exist, was a hassle and involved traveling and like happened once a year, if that.
You just adopted a playing style that could exist among your friends and family.
Melee added villains from the series that didn't exist in 64.
We had Bowser, Ganondorf and to a lesser extent Mewtwo.
This really circumvented the desire for villains, hence Ridley and King K. Rool.
Ridley was in the opening trailer at a playable size so he went popular for a brawl candidate...
K. Rool was just another popular reoccurring villain, also note the Donkey Kong TV series was on television around this time with K. Rool as a popular villain on the show.
I feel Black Shadow was also just as popular because the F-Zero series was more relevant back then, but he some how fluttered in comparison to Ridley and Rool.
So no Ridley, Rool, or Black Shadow in brawl was also a let down ontop of the Roy and Mewtwo cut.
sonic was huge for brawl though, because that whole magazine april fools thing for sonic and tails in melee.