Super Mario All Stars was one that I borrowed from my friend. It was a great way to enjoy the original NES classics on the SNES.
I was never able to borrow Mario Kart from my friend, because it was one game that he would not loan out. But I went to his house and played many hours on it. I remember trying to master that shortcut jump in the haunted house level using the feather. Very fun game to play solo or with a friend.
The Donkey Kong Country series was one of my most beloved game series. I was also blown away by the graphics when the first Donkey Kong Country came out. But the difficulty jump from the first game to Donkey Kong Country 2 was no joke. DKC2 was hard...
The retro arcade on the Switch is awesome! Like you said, it allowed me to play titles I didn't play back then. My kids also play on it and love some of the old classics.