I've been playing Super Mario Bros. 3 and World on the GBA in random bathroom spurts. I never had an NES or SNES as a kid, so I didn't get to play them as much as everyone else, but I still loved the games, and would play them when I could.
I still think they're some quality games, but not as good as I remember. I think Yoshi's Island is the reason for this because it's the game I compare every 2d platformer to and it's really hard to top. The Mario's before YI just feel so drab in comparison.
SMB3's levels feel too short, and SMW's platforming isn't as fun.
I can go back to SMB1 and SMB2 US just fine, but 3 and World just aren't as fun as they used to be.
Final Fantasy VII is probably the biggest candidate for this thread for me though. I used to praise that game so much and then when I started to play other rpgs outside of Final Fantasy and Square, I kinda realized how mediocre it is, and these days I can't stand playing it.