Star Wars: Knights of the Old Republic 1 and 2
Pokemon Yellow and Pokemon SoulSilver
1. Final Fantasy X
2. Final Fantasy VII
3. Golden Sun
4. Pokemon Red/Blue
5. The Elder Scrolls: Oblivion
FFX was my personal favorite, gorgeous music and visuals really helped to immerse me into the world. Voice acting was atrocious, however.
FFVII is there simply because it's a classic. I played it after FFX, so it was extremely hard for me to accept the polygons, couldn't immerse myself into the world as easily, though I can see how it was phenomenal back in the day.
Golden Sun absolutely amazed me as a kid with its story, visuals, and gameplay. Probably one of the best looking GBA games to date.
Pokemon was a key player in my childhood, and probably one of the first games I spent hours upon hours playing. Sleepless nights under the covers with a flashlight...mmm...
Oblivion was SUCH a huge step up from Morrowind, I spent hours just walking across the land and admiring the different textures because it was so beautiful. I upgraded my graphics card JUST to play this game when it first came out.