That's fully understandable - you were 10 - 12 around Brawl's development and reveals yes? I was smack dab in that age range when Melee came out (and I got into Smash). I had the same kind of reasoning and opinions around characters then.
Now, disclaimer time: Melee's base roster was revealed at E3 2001 and the unlockable characters were unlocked through play-time with not much prior knowledge or via word-of-mouth. Back then I didn't know E3 nor Melee existed, and I was an ocean away playing StarCraft I. This was also right before the Internet got reliable (and cheap, I recall my parents' "30 mins Internet time max per day" rule) enough for frequent use, so not many looks there if at all. I remember getting Melee together with my elder brother June 2002, and I'm going to rank my first impressions of the newcomers post-release:
S:
: Mewtwo was
the Smash character for many kids then. Me included, The 24-hour unlock requirement just added to his mystique. And yes, I remember the OG Pokemon craze. Get off mah lawn!
A:
/
: "A unique transformation-based character? Neat! Controls weird though, but she's still great."
: I quickly learned to love his jump arc and down-airs.
: Quickly became a casual favorite because of how hard he hit.
B:
: "Another unique character! Shame that their stage is so bad..."
: Was expected, but 11 year old me was still impressed by his moment in the opening (okay, the entire opening. This was with my love for the Matrix still relatively fresh. But still.). Was used decently often, and his Giga Bowser transformation was an actual shocker (no pun intended).
: Another expected character, but the RNG Turnips and her general moveset made her fun to play casually. Not many strong opinions otherwise.
: "Who is this dud- Oh whatever, he controls great!"
: "Huh, another one? At least he seems more energetic, still like him!" Didn't know he was promotional until years later obviously.
C:
: My 11 year old self made the connection to then-current Pokemon 2000 and knew this was a promotional pick.
: Felt kinda strange to have two Links - and I didn't know about Majora's Mask. Thought it kinda neat to represent OoT fully though.
: "A 2D fighter? Okay, wait, his stage. Oh, I get it!"
D:
: "Huh, Mario in a Doctor coat? Why?" Still became a casual favorite down the line.
Depends, if we get someone from an FPS, maybe the often discussed Master Chief or Doom Slayer could count. Though Halo's about as violent as MGS. Travis Touchdown's been a fairly popular choice since around the later Brawl days from what I remember. And Mortal Kombat would always be welcome in my book. I think KI was always T rated, but I forgot the rating for KI1 and KI2 off the top of my head.
I think SMT is also M rated, so there's that too.
*Coughs in Gordon Freeman*
Nah but seriously, agreeing with this. I'm also going to add Kratos and a StarCraft character as "Small chance, but kinda present." possibilities. Obviously no frontrunners, but not out of it really.
Also, looked it up, the SNES KI was apparently rated Teen, Killer Instinct 2 (or Gold) also Teen.