Melee was my first Smash game, and I was about 9 when it came out. I recognised:






Recognised them from
Mario games and spinoffs




My brother and I played
Red and
Blue when they came out and were big fans of the anime

I had played
Oracle of Seasons and recognised Link from magazines
Kirby was my favourite series at the time and my very first main


My brother and I played
Lylat Wars religiously when we were little
I had a vague inkling as to who these characters were:

I knew he was Mario, though I had never played
Dr Mario

I knew Zelda was the title character in
The Legend of Zelda, though I had never seen her before

I knew of Game & Watch, didn't know that's what he was supposed to be at first

I caught on fairly quickly that he was a young version of Link (you don't say?), hadn't played
Ocarina of Time
I had no idea who the following were:

Never heard of
F-Zero, I thought he was a superhero of some kind

To be fair, I doubt most of us knew who these two were

Not a clue

Even less of a clue

I saw the name "Ness" and thought he was either a young Mario or an anthropomorphic personification of the NES

Yeah, I thought "he" was a robot, though it wasn't the skeleton that clued me in - it was the all-female fighters event

Absolutely no idea, though the opening cutscene hinted that she was a
Zelda character

Didn't know either, didn't realise until after he'd been unlocked that he had a cameo in the opening cutscene
When
Brawl came around, I was a tad more knowledgeable, and of the newcomers, I recognised:

My most-wanted newcomer at the time,
Wario Land was one of my favourite series when I was little

Recognised him from magazines and spinoffs





My brother being a huge
Pokémon fan, these came easily to me


Again, I was a huge
Kirby fan in my youth and recognised these guys instantly

Loved
Wind Waker, and he's also my favourite incarnation of Link

I had heard of
Kid Icarus from magazines and was familiar with Pit as a character

I had played
Zero Mission and recognised her from that

My brother played
Path of Radiance and I recognised him from that

I had played
Pikmin 1 and
2 and was delighted to see him in the roster

Again,
Lylat Wars, though I knew he was in the game due to hint guides

I recognised him from magazines, and he was my favourite character in
Mario Kart DS
My favourite thing in the universe as a child, this goes without saying

My mother (yes, you read that right) was a devout fan of
Metal Gear Solid 2 when it was first released
The only newcomer I didn't recognise was

, though I figured from the design that he was from the same game as Ness.
I recognised almost every newcomer in
Smash 4 and was actively involved in speculation for the first time; the only one I wasn't familiar with was

, and while I had heard of the
Xeno series before I knew of Shulk, I didn't hear of the character until I started speculating and didn't know anything about him until his trailer.
EDIT: Forgot Diddy. Says something, hm~?