World of Warcraft and EVE Online both have extensive information available about the numbers behind the working of the game.
On the other hand, people have complained that the emphasis on numbers turns the game from an exercise in play and experimentation into differential calculus. And there's certainly room for games like Final Fantasy XI, which gives enough information for comparison without going into detail about what a given value actually does. On the other hand, by removing contextual comparisons, it becomes difficult to figure out what effective difference there actually is between Accuracy +3 and Accuracy +5.
So which do you prefer in a game? Would you rather tend toward having all of the numbers laid out in front of you, even if it means needing ornate spreadsheets to enjoy everything? Or would you rather keep as much of the system as possible under the hood and invisible?