The quality of game content (with the exception of music) has only gone up. This has a direct impact on gameplay, especially in immersion type games which focus heavily on environment.

Personally, I don''t like the old games. I like Thief, I liked RTCW (It had a cross between old and new style gameplay, immersive graphics, and just enough of a storyline. I only wish it had been longer), and I like many RTS games. All of these take thought and planning, and immerse you in an environment.
Can you say that for Galaxan? For space invaders? Those two examples are fun for a little, and then just become repetitive automatic-reflex twitching. Sneaking around a corner with a sniper rifle requires a different kind of concentration, and one that is much more enjoyable.

In other words, games have improved.