My two favorite games of all time are Pokemon Sapphire and Wind Waker. I spent so much time just adventuring and exploring the beautiful worlds in both of those games when I was around 10. (If they remake Ruby and Sapphire on the X/Y engine I will probably die of happiness lol). Wind Waker is just so beautiful and has so much personality, even the GC version is still beautiful 10 years later.
Also, even though I was a 90's kid Sapphire was my first Pokemon game because my parents wouldn't buy me Pokemon lol. I think starting with Sapphire gave me an appreciation for the newer ones that a lot of kids my age don't have. I also went back and played Crystal around that time so gen 2 has a special place in my childhood as well, it's just in the wrong order lol.
My favorite game for entirely nostalgic reasons is Sonic Adventure 2!! Around the same time as the others I spent hours and hours playing through this game, replaying my favorite levels, taking care of my chao. I went back to it in college and got all the A ranks, which was one of the funnest things I've done in a game. However, I do recognize that objectively this game ain't that great and has not aged well lol.
I also recognize in my list the Mass Effect series, because it does so many things right story-wise and protagonist-creating-wise (surprised more games haven't improved this yet).
Another favorite is Persona 4, again because it does storytelling in an exceptional way and it's incredibly fun of course.
Edit: sorry for the novel I just have so many favorites for so many reasons and I enjoyed typing it all out.
