I recently finished playing Professor Layton and the Curious Village. Yes, the first Layton game -- I haven't had my DS for very long and have a lot of catching up to do.
I've been thinking about what makes a puzzle satisfying. Too easy and it's not really worthy of being called a puzzle. But too hard and I'll soon check a walkthrough rather than fruitlessly bashing my head against it.
Everyone finds different things challenging, though. For example, my partner has me well and truly beaten on number problems, while I have an easier time with spatial puzzles. Puzzle difficulty is quite individual. That said, I've yet to meet someone who didn't consider that map puzzle in Riven too damn hard. If you have played it you'll probably remember the one I mean.
Another common problem with puzzles is lack of detailed localisation. I sometimes need to stop thinking like an Australian. I forget that what I call the first floor of a building is the second floor in the US (and presumably Japan?). Date formats and holidays also mess me up sometimes.
These cases where my nationality is a detriment to gaming are relatively infrequent in the scheme of things, but it’s something I’ve been quite conscious of recently. I dread to think how often game puzzles assume things like normal colour vision. That's not something I'm likely to notice myself.
(Actually, I take back what I said about my nationality only rarely being a problem. Delayed release dates and over-pricing are a constant disadvantage to gaming in this country. But that’s another issue, and one that’s been tackled much better elsewhere.)
I'd include age as a factor making appropriate puzzle difficulty harder to set, but honestly I was way better at this stuff when I was younger. My skills in basic maths and puzzle-logic have atrophied over the years. Provided you are old/educated enough to understand fractions you'll probably do as well or better than me.
A game like Professor Layton contains a lot of puzzles of course, so I think it gets away with the potential problems with game puzzles relatively well. Only a couple put me at a disadvantage for being an Aussie, and with that many puzzles at least some were bound to have the right level of challenge.
I suppose the hint system is one approach to making the challenge level appropriate for a broader range of people. But I found that was usually either no help at all or practically gave away the answer. Writing good hints must be at least as difficult as coming up with good puzzles.
This discussion is probably coming across fairly negative, and I don't really mean it to. It's precisely because of all these issues I admire good examples of puzzle games. There is a good reason for Professor Layton's popularity. It's probably dealing with the difficulty issue almost as well as a game of this type ever could.