About the XCOM vs Mario(and most other games) in terms of failure, and forgive me for pulling that one point out of the context of a larger discussion, but there's a huge difference. Because of the way it is structured, to use Chris's phrase, "decisions that ripple forward", it's entirely possible to flat out lose a campaign that lasts longer than a lot of action games. You don't have to be playing on ironman(one save forced on you after every move, no reloading) like Chris to run into it either. You could be reloading every mission and decisions that you made a month ago(game time) will come back to bite you, possibly accumulating to a complete failure or to a point where you might as well throw in the towel.
We can debate the merits of this kind of design, I think it's very interesting, but there's no denying that doesn't happen... almost ever. It would be like Halo 4 declaring, "Well well, Master Chief. I see you didn't pick up that laser cannon back in level 2. You could keep retrying level 6 or reloading back to 2, but you may as well start over." Not that XCOM is that cheap and unfair or the choices that plainly right and wrong, but that's the sort of thing it can come down to. Even in a huge RPG, let's go back to an early JRPG because recent Bethesda games and such have done away with even this kind of setback, you can simply retreat from a boss and grind away. Come back to fight another day, Brazil isn't gonna quit on you in Final Fantasy, forcing you to operate at a monthly loss, leaving you essentially stranded.
It is really more like a chess game, you can make mistakes at any point that may prove to be fatal. Maybe there's a chance, if you're good enough, to come back from it and change the tide, maybe you can't. Most games will simply reload you back to the point where you made a mistake. Or maybe you can sit in a corner, behind cover and regenerate your queen. Better yet, you only ever should reward the player! fun! fun! fun! Anyway, just expanding on the point Chris made...
