Way back in the day my brother and I beat TMNT: Turtles in Time. I was 5 years old so at the time that was pretty amazing feeling. 

others was

Goldeneye (n64)

Super Mario World

Mario 64

Secret of Mana (snes)

Half life 2

Gears of war 1-2 (all you do is go striaght lol)

and recently Super Mario 3d Land.

Yours?

Super Mario Bros. in 1986.

My 1st game ever without looking up anything ever?

Prolly Super Mario Land.

Crash 3. 100% completion in 1999 (got it Christmas 98 along with my PS1)
Spyro 1 I beat first but not 100%, in fact I didn't go back and finish it until I got it on PS1 classics this past Summer so it only took me 14 years lol

Dragon Warrior for the NES.

But the one im most proud of is Phantasy Star 2 for genesis. The game was so hard that it came standard with 110 page hintbook. I bought my copy used without the book. Took 6 months to beat.

Pokemon Green. First game I ever beat too.

The first game I ever owned, Pokemon Yellow. I still remember my first Lv. 100s, Zapdos and Pikachu. I hate myself for selling that game to help buy my 3DS. So many good memories.

Marble Madness then Super Mario Brothers. I remember throwing Mario aside because Marble Madness looked so awesome.

my first game was the lion king on genesis back then I was 5 years old. that was not the only one. I bought my first magazins with the n64 so on all games before I hadn't any guides.

Starfox on the SNES. Good times...