by clivej
but since you say you did not find Forbidden Desert challenging and you had not played it before, I have to wonder. Did you play by the correct rules?
I feel there's a subtle difference between "challenging" and "difficult", here.
I've played Forbidden Desert, um... three times, I think? I know I've played it at least twice because I recall both winning and losing. Either way, it certainly felt as though the strategy was obvious and railroaded: all we had were some tactical decisions to make, which weren't especially deep. Luck played a considerable part in whether we won or lost. That's difficult, without being challenging. Still fun, though.
Pandemic also has a lot of luck in it, but it's balanced so that there are many credible strategies, and lots of opportunities to do something about your luck, whether good or bad. If things are going well, there are safety plays you can make to "lock in" your win; if things are going badly, there are calculated risks you can take to try and recover. The game feels challenging, and the good or bad luck in any individual game feels like a randomised difficulty setting rather than the main determinant of whether you win or lose.
Pandemic Legacy preserves, even enhances, that sense of challenge. Plus, there's a different kind of challenge: each new mechanic "matters" at once. There are no dry runs; you don't get to practice with them before they have a lasting effect.