I'm out of town for a weekend, and then a topic like this has to happen. Okay, let's set some stuff straight.
Let's just start by attacking the biggest myth in the community: that Melee is better balanced than Brawl. I could offer many logical arguments for why this isn't true that no one would believe so instead I'm going to rely on straight tournament results. Just check out smashboards rankings and go to the character sections for each. As of about 5:30 PM CST today, I did a little math with these numbers. Consider:
Code:
Brawl: 4169
Meta Knight: 16.77%
5% count: 4
2% count: 17
1% count: 29
Melee: 9380
Fox: 18.43%
5% count: 6
2% count: 12
1% count: 13
The top numbers for each game are the total number of points per game, a measure of the popularity of the game. Brawl is about 44.4% as popular as Melee, but the important point for our purposes is that this is the denominator for all viability calculations. Taking the total points a single character has divided by this number for the respective game will show the percentage of the metagame that character controls. Right off the bat, we see Meta Knight actually controls somewhat less of Brawl's metagame than Fox controls of Melee's which is very interesting. Melee's number of characters who control at least 5% of the metagame is 6 to Brawl's 4 so Melee has a larger top tier. However, the number of generally strong characters in Brawl (2% of the metagame) is more like 17 (almost 18! Peach was super close!) while Melee has only 12 which is a result that shows a nearly identical percentage of each game's total cast in the "high tier" strength level despite Brawl having a considerably larger cast. Then you look at the 1% level which is about the level of "any real viability at all", and Melee adds only one character to have just 13 characters and half the cast while Brawl shoots up to 29 characters which is 78.4% of the cast. There are a lot of interesting things that could be said here, but just saying that Brawl is worse balanced than Melee is flat out not reasonable. You either have to insist that the tournament results for these games are bogus and totally unreflective of how the games really are (a very dubious claim in two old games like this!) or admit that we have an interesting and nuanced situation here that honestly reflects pretty well on Brawl as a whole.
For smash 4, the main thing to take away from that is that Sakurai's prior efforts are actually pretty commendable, and his ability to balance has only been improving game to game given that he scaled up to Brawl's 37 character roster remarkably well. If nothing else, he doesn't have to redeem himself after the past game on the question of balance so there's no reason on that front to be skeptical of the balance of a further game.
Then we can look at our other main data point which is the impressions from everyone who has played. They've been pretty universally positive! Most people who had positive demo impressions (myself included) gushed over the balance. We had a few minor complaints on it (Zelda really did seem to suck), but for every complaint we consistently had high praise for so many other good decisions like how every other low tier who really needed help seemed to have gotten it (Yoshi, Bowser, Mario, Samus, Link). The negative impressions of the demo seem mostly focused on people disliking gameplay systems like dash mechanics or shield speeds or whatever; I haven't actually read a single one that said "it seemed like only a few characters were any good" or anything like it. People often focus on what HugS said, but as I understood it, he was just saying he was sure Samus was not the best character in the game, a statement most of the community agreed with him about and a statement that says absolutely nothing about the overall balance of the game or even about whether Samus is overall a good character. Likewise even when we buy into the arguments from credibility that suggest listening just to players with a strong tournament history to the exclusion of everyone else, the main impressions I remember seeing were zero's... which were pretty positive as I read them!
I truly just don't get why people would be down on this point at all; it seems to me like every way there is to look at this issue should lead us to be optimistic about the balance of the new game. We won't know for sure what it is until we actually play and for more than a year really, but all sights so far are really positive. I would say that, yes, we can and should trust Sakurai and the dev team to do a good job on balance; they've given us no reason to suspect they'll do anything less.