A big part is that we only remember a handful of excellent older games vs. the entire catalog of today. See the AVGN to see some of the crap inflicted on the children of yesteryear.
The second part is that gaming was more innovative back then. Of course, that's not entirely fair because there was more room for improvement at the time. You can only invent things once, after all.
A third part is that games back then were simpler and more devoted to a few gameplay elements. An extreme example is Tetris. Another one would be Legend of Zelda; you wander around, collect money, buy stuff, and see what you can do with it. There's no attempt at cutscenes or moral choices or cover mechanics. In modern RPGs, characters often have two dozen statistics, hundreds of pieces of equipment and enemies, and elaborately choreographed battles and cutscenes. There's more complexity, to be sure, but actually using it requires vastly more effort and can make the game a chore to play. Nostalgic games tend to be simple.
The second part is that gaming was more innovative back then. Of course, that's not entirely fair because there was more room for improvement at the time. You can only invent things once, after all.
A third part is that games back then were simpler and more devoted to a few gameplay elements. An extreme example is Tetris. Another one would be Legend of Zelda; you wander around, collect money, buy stuff, and see what you can do with it. There's no attempt at cutscenes or moral choices or cover mechanics. In modern RPGs, characters often have two dozen statistics, hundreds of pieces of equipment and enemies, and elaborately choreographed battles and cutscenes. There's more complexity, to be sure, but actually using it requires vastly more effort and can make the game a chore to play. Nostalgic games tend to be simple.
