Captain Falcon Match: That was intense stuff. I really enjoyed that. You made Samus move all quick and everything! Samus' normal approach would be firing Homing Missiles and using z-air. You only used z-air twice in that match, and I don't even recall you ever using Homing Missiles. Not that that's a bad thing. You did quite well without the use of Homing Missiles and z-air. Try to save your Charge Shot until your opponent is at a good percent to be KO'd. The only time you should ever use it is in desperate matters. Oh, and if your opponent is standing over at the edge while you're hanging on it, use f-air when returning from the edge.
Diddy Kong Match: There's one thing I have to say: counter-pick. That stage looks like it did wonders for your Samus. Diddy Kong was gimped twice by the lava below him, and because there is more jumping around on that stage, Diddy Kong was unable to use his Banana Peels against you. It's a shame you lost on that stage, of course. Like I said, in desperate times, use your Charge Shot. You had it fully charged in this match, and you could have used it.
Sheik Match: There's one thing you should always keep in mind about opponents who lack reflective, absorption, or counter abilities: they're easy targets to hit to hit with projectile attacks. Sheik's f-tilt has nothing on Samus, as well as a few other characters. Since this is about Samus, you should be aware that Sheik's f-tilt cannot lock you in. Of course, your opponent only used that twice and then would use a different attack, which probably means that he was aware of this.
Earlier in the game, you were on the edge (0:33-0:35). Again, use your f-air, especially if your opponent is going to be jumping around instead of shielding, standing back, or anything else that will prevent him from getting hurt. You did it later on in your match, but you were at high damage. Also, use more projectile. If you start firing Homing Missile after Homing Missile, you will create a wall against your opponent. Other than that, for one who plays as Samus casually, you seem pretty good. As for the Marth matches, I didn't watch those. Sorry.