I never played the original or Melee, but got myself into Brawl.
Jigglypuff is an alright character, though I would prefer others like Fox, Falco, Kirby, etc.
The "Rest" move only works at a real short range (like if your opponent is directly over you, then PING!!!) and otherwise costs Jiggly time in sleep.
Also, if Jigglypuff overuses the shield, then kiss it goodbye unless there is a ceiling above it.
Still, there is that glitch in Brawl that is fun to play with. Give Jigglypuff the Smash Ball, and use it when the bridge regenerates in that Zelda arena. Then get Yoshi to repeatedly swallow it, and get GigaLuff!