One thing glaringly stood out to me, which I couldn't believe that you SSB players forgot..
Referring to the D-Pad as a verterans tool couldn't be farther from the truth in this game. Suppose they were to implement it, then you'd be reduced to performing smash moves with your C-stick, making them all the same frequency in power, and on the flip-side, no strategic powering up. That can win or lose a match for a veteran.
The universal appeal of Smash Brothers is wonderful, however I think there is a much deeper game here than anyone can imagine. I, and my friend have clocked in well over 460 hours of VS. match time, 500 hours total system power on time. A game that is seemingly so simplistic could not be played this much, this often. I am in no way comparing this to a fighting game such as Tekken or Soul Calibur, but the similarities in strategy are fascinating.
Firstly, knowing about each weapon is key in this game. For instance, if you are Falco (whom i play with) or Fox, you have to know that while you can reflect (Down+B blue shield) beam swords, bombs, shells, etc, (pretty much anything that can be thrown) you cannot however reflect a star wand being thrown. You can, however, reflect the star propelled from a smash moved-star wand.
Secondly, using smash moves in this game adds a whole new depth factor. This game can be a button masher, people. But it can also be a very intense game comprised of defense and offense. Timing a smash move can be one of the most effective tools in this game. It racks up damage much quicker than any regular hit, it throws your enemy on the ground generally (which stuns them for a brief second) and you can hit them off the stage (when they're at a high percentile) quicker.
Third, the defensive strategies. I find that half of my battle is composed of mid-air dodges, rolls, what i like to call "grey reflections", blocking, reflecting (if your character supports it), catching items in mid-air, etc. Deep, deep, deep.
Fourth, using the stages as an advantage. This is where i disagree with one post. Yes, it's great to have a couple stages with some huge interaction, but i find them to be mostly annoying when you are wanting to actually have a skilled fight (yea, the Pokemon floats stage comes to mind... ). Stage advantages (so called, home court advantage) is great when fighting other players. Knowing, for instance, that you can double jump across the bottom of the Termina-Great Bay stage. It's a useful tool in combat.
Now, on to my gripes of the current game that they could improve on..
1) I assume that this is due to perhaps this being a first generation title, or perhaps the fact of the Gamecube RAM limitations, but the AI needs to be tweaked dramatically.
A) During VS battle fights, if you are playing a stock match. For example, If you, a friend, and a computer player are fighting, say your friend was just defeated. This once "level 9" computer opponent becomes a punching bag, for whatever reason. They just become literal idiots. I'm not sure why. Fix that.
B) The game seemingly has a "dice" system.. my belief is that when you begin a match, the game decides "OK, player 2 will have explosive pills and party balls open with bombs over his head. Now, i know that a pill has a .. i think 12% chance of explosion. OK. But honestly, many, MANY, random things, ridiculous things, happen to one person per match. While this does add to the overall unpredictability of the game, it should be spread out evenly, to even *gasp* the AI opponent.
C) Get hammer. Watch computer run to opposite end of stage. Watch other human opponent approach computer player. Watch computer player do nothing. Watch other human whip the computer players ass, while he just stands there until your hammer expires. The same goes for a star, and bullet bill on the Princess Peach's Castle. Yes, they should avoid you at all costs, but if they are being attacked by another source, they should also predictibly defend itself from harm, which usually involves leaving that section of the screen.
D) The CPU has no sense of the proximity mine. It will walk right into it. Always.
E) *Some sort* of random action should be instituted on the computer player when the pokemon darkout occurs. He sees VERY well in the pitch black, apparently. =/
2) Include the tournament option, add more options to it, and make it LAN capable, as was previously posted. Kick ass.
3) Improve SOME of the character models and definitely institute harsher anti-aliasing tactics.
4) What can they do with sound? It seems as if they can NOT beat this soundtrack on this game. The next game in the series has a HELLUVA lot to live up to in the sound department. And oh, HAL, by the way, *coughSpecialPre-orderBonusDiskWithTheFullGameSoundtrackcough*
5) Keep to the Nintendo cast of characters. Outside sources remove the whole feel and the mood of the game. Sorry, this is Nintendo territory.. no FF characters, fanboys.
6) Please, oh PLEASE improve the ending movies for all of the characters. What was that super-compressed crap-ola at the end of the game? And further more, whats up with shooting all of those names and getting nothing as a reward?
7) Drastically improve Adventure Mode. This was such a great addition, but it should not be able to be completed in one sitting. I would like it to actually be like an actual Mario game of sorts.. They had a great idea, but expand on that. Make it more rewarding, *ADD SPECIFIC STORYLINE ELEMENTS PER CHARACTER*.

They've done the trophies, now what? I'm honestly not sure. The trophies idea was one of the most ingrossing, challenging additions to any game, ever. Having this living Nintendo museum makes this game a keeper for many a year after the GCN's life-span is depleted. Perhaps, now that the trophy idea is gone, they could focus on the story part of the game, like i said before, adding specific story-lines per character, instigate in-game rivalries, etc.
9) More event matches! One of the best (and most challenging) aspects of the game. How great were these matches... and creative to boot. Twice as many.. or at least make them with multiple difficulty levels.
10) More weapons, each with a distinct advantage/disadvantage, allowing for a strategic weapon match system as far as gameplay goes. Say the ray gun was weak against a certain new weapon simply because it could reflect it, or perhaps it is a rapid fire so it disrupts your shots, etc.
11) This might be lofty, but i wants all damn 251 pokemon or however many there are in this game. I have gotten so many of that "Goldeen" or whatever its called, and the blue pokemon i tentatively deem "slappy", it almost gets annoying. Pokemon are an intricate part to this game, they add a lot of fun and unpredictability. OK, OK, maybe not all of them, but at least triple the amount that are currently in the game.'
12) MAKE THE SCREEN CAPTURE FEATURE ACCESSIBLE IN NORMAL GAME PLAY. This was such a wonderful addition to the game, but it was awkward because you actually had to go to a "Screen capture" mode to actually use the camera. I have had so many funny and awkward moments in my play history that I almost make this my number one plea.
13) KEEP IT IN two dimensions. PLEASE.
Minor gripe: make the percent numbers and "life heads" at the bottom of the screen semi-transparent. They can sometimes get in the way.
I'm in no way a professional video game designer, i just play them. But, i feel that making these improvements would make an already outstanding game even better. And i feel as if I have only scratched the surface. This is a long post. I'll stop now and go play some SSB. Later.