Here's a little puzzle for you:
A couple of years ago I decided to fill two holes in my gaming history and played through System Shock 2 (released 1999) and Deus Ex (2000). I had never played those games, I was about 18, so no childhood nostalgia or anything. The stories they tell are alright, but they're game plots. Especially Deus Ex has some horrible balancing problems, they both look pretty awful (you know, the early 3D), the game mechanics are fairly simple and so forth.
But they both just hit me like brick in the head. I enjoyed them from start to end and even more importantly, they got me immersed, got me interested way better than any of the new games I'd played in a few years. I just didn't want to stop playing, I sank in and stayed there.
I've been trying to figure out what's causing that, but I can't really grip it. Not precisely. The best I've figured out is that when I play a modern game, I take the attitude that I'm here to be entertained, entertain me. Deus Ex and System Shock had some bad flaws, they were at points difficult in very stupid and seemingly frustrating ways (limitations of the game mechanics, for example), but I didn't care. I took it as a challenge. This game is like this, are you gonna beat it or not? I think you could say that the old games gave a feeling that they don't care if you like them, their purpose is not to make a pleasing experience. They create a world, put you in a situation, give you some tools and set some limitations and say "there you go, I hope you like what we made".
Somehow new games fail at this. Some of them are pretty difficult, often in a lot more sensible ways than the old games (I mention this because some people argue that it's just that old games were challenging, it's not that) and mostly I just find it annoying. A lot of them are straight pipes or rides where you just push forward through the one door that's not permalocked, but so were many of the old games. Some of the newer games create amazing open worlds, but that still doesn't do it. There's something (let's call it the X Factor) in those old games that just makes you look at it and think "let's see what this one is made of" instead of "let's see what kind of an experience they have prepared for me today", and I can build a web of related things around that factor but I can't point out the core of it.