Interesting. This touches on a question I've been musing on lately regarding games as escapism (are they really? Most people seem to think so. Should they be?) Maybe I'll expand upon this thought later when I have more time.
As far as a direct answer to your question, I've noticed particularly as I've grown older that I do indeed enjoy games less. I've also grown cynical about why others play them as well. My current viewpoint is that most games really are hacking into our psychology to make us keep playing and keep buying - they've become a well-designed set of reward schedules. There is a very compelling literature on this in psychology, about how reward schedules (particularly variable schedules, where you know there's a reward, but not exactly when it will come) are irresistible to lab rats and people alike. Basically, the reward is dangled in front of you (shiny set of armor + nasty sword), and you jump through hoops to get it. But does anyone else notice the empty feeling that comes with finally achieving the reward? It's my guess that people grow out of these games when they start to recognize that, while others simply clamp on to the next reward and set of hoops without questioning it.
For me, the things that tend to give me true enjoyment are the beautiful (aesthetically) things that you can bring into existence from time to time. For example, in a Final Fantasy game, I might earn a powerful spell that has a beautifully rendered effect when I cast it. It's part of the style of FF games to make these very elaborate, almost like a little show that you can create every so often. I like those

There is also no question that you can feel a sense of accomplishment from overcoming a challenge, though this is also an effect that sits in a psychological sweet spot. The idea of "flow", where difficulty fluctuates perfectly with the player to reward accomplishment, while always remaining just challenging enough (maybe I didn't explain that well, but I'm sure people here are familiar with the concept). I don't like feeling like a game is manipulating me, though I now wonder whether my intellect, in recognizing that, is possibly robbing me of some honest fun.
Anyway, I learned long ago not to project my cynicism on others, or assume I know how they work. I'm interested to hear what others think.