Can you tell me what your current opinions are (of those you have formed) about Samus's matchups in BBrawl? Who does she still struggle with the most, or what characters have gained the most to use against her? My impression is that Samus will always be at a relative disadvantage against smaller, faster characters that she has more trouble controlling the pace of the match against. (Squirtle might actually be her worst matchup... although she does great against the other two Pokemon.)
Crescens pretty much nailed it in terms of which characters Samus has a noticable disadvantage against. Smaller, quicker characters are her weakness.
In BBrawl, Samus has a large disadvantage against: Diddy Kong, Toon Link, Meta Knight, Olimar, Pikachu, Squirtle, and Mr. Game and Watch. Samus has a slight disadvantage against: Luigi, Sheik, Kirby, Fox, Falco, Wolf, and Marth. Samus is pretty much even with: Peach, Donkey Kong, Yoshi, Wario, Link, Ganondorf, Pit, Ivysaur, Lucario, Ness, Snake, and Sonic. Samus has a slight advantage against: Mario, Bowser, Zelda, Zero Suit Samus, Captain Falcon, Charizard, Jigglypuff, and Lucas.
I left out Ice Climbers, ROB, and King Dedede purposefully. I have not been able to decide their matchup with Samus because the CPU sucks just that badly, and because I don't have much experience with their normal Brawl counterparts.
I was thinking of a way how to improve her bad matchups when it hit me: what about her up smash? By severely decreasing the overall power of the move (maybe like 5% total, 1% per hit), decreasing the knockback of the last hit, and adjusting the move as a whole so that it works kind of like her fair, would, in conjunction with her 'initial dash animation cancel up smash slide,' provide some protection against many aerial approches that Samus' bad matchups have. At the same time, the move would be so weak damage-wise that it would not be viable for anything much other than aerial defense (unless perhaps in addition to the weakening of the last hit's knockback, the knockback's direction was changed to combo in to screw attack or something, but that kind of defeats the purpose of it being a defensive move).