I was pretty shocked at the rate of change in Crawl. I played it for a couple of years and during that time entire major game mechanics changed, like moving from many kinds of food, to only one kind of food, to completely eliminating food and hunger (while adding a completely new form of clock to kill players who didn't keep moving).
Why was the rate of change so huge? And the changes so deep? These roguelikes particularly tend to be stable, almost frozen - at least in terms of mechanics.-