Fully aware that many of you will say stuff like "NOOOOOOOOOOOOOOO" and so forth, backup is required:
Not facts here, just opinions/thoughts:
Melee may have more stuff to offer, but to me, it feels like the controls are really loose compared to N64, which makes it tighter and more ground-in. I feel like my "focus point" is right behind my character and that they feel like they're floating around when jumping. And most attacks aren't as hard-hitting as they were in SSB64. It also tends to outright overdo the whole frantic factor. Too much going on on-screen, it's like hard to understand what exactly is going on there. Some characters' attacks just aren't as hard-hitting as in N64 either.
Some characters tend to get watered down. Kirby has been messed up a lot in Melee compared to N64, as many people would know. I used to be really good with Luigi in SSB, but they mangled him HARD in SSBM.
Other than that, what actually made SSB shine compared to SSBM was that there's more balance among the characters in the N64 edition. Some got too overpowered in Melee. Like Captain Falcon.
Plus, when I went through Melee's supposed "Adventure Mode", I was completely mortified. I thought it would completely focus on the side-scrolling part, but there was only one bit of that. All the rest, normal fighting. It also had quite a weak presentation, at that.
Melee may have more new characters and areas and all that, but does that necessarily mean they're ALL good for being new in there? SOME of they may be, but others aren't. Especially certain items.
Levels, too. The majority of them were too small, really. Yes, even lower than "medium". "OMG HYRULE TEMPLE"....Shut up. That one level was blatantly terrible and overrated...or should I say, overplayed. Some of the moving stages, too: some were alright, others tended to be downright frustrating. When you're stuck with one opponent, you may both involuntarily get consumed by autoscroll. Too much moving against the area can take the fun out of going for your foes, too.
Don't get me STARTED on the graphics. They look sharp yes, but is that what has a great impact on the gameplay in itself? I think not. All in all, 64 tends to shine some in the tight, distinct gameplay department.
Hopefully, Brawl should be able to bring back the GRIP that 64 had.
Heck, both games are equally good. Brawl will be the same as well. No game is ever perfect, really.