I never experienced the NES generation, because I was too young for that. I'm a nintendo 3DS ambassador, so I have a couple of NES titles now. I find most of them horrible. They are just simply too hard.
I love a hard game though, but it should be hard to beat because of the right reasons.
The reason I find the NES games hard is because they are often very unresponsive. Controlling Mario in SMB is so frustrating, compared to the newer titles.
But for example, with a game like Super Metroid I never had a problem. That game is also very hard, but because of the right reasons. It is challenging, but not annoying, and the controls are responsive. The game is hard, because the enemy design and level design are designed that way, and not because of a technical shortcoming.
So yeah, I can finish hard games if they are difficult because of the right reasons, and not some annoying limited capability.
I also love that the games are now easier/friendlier. I have an aunt who is now 56 years old, and she started gaming about 5 years ago. The first game she played was brain training, and her first "real" game was NSMB. Now if it wouldn't have been for the perfect controls in NSMB she would have never experienced how fun videogames can be. She now also plays Super Mario 3D Land, NSMB2, Luigi's Mansion.... Heck she even completes them 100%. So yeah I'm all for multi-layered games that are easy at the start, but offer a deeper challenge for more experienced players.