One of the developers of Steambirds: Survival, Danc, has a pretty interesting blog post about Steambirds and something he calls the "Arrow of Play". In his own words Arrow of Play "is a directional property of the mechanical systems that always moves the player forward. And like time, there's often a surprisingly amount of variation that occurs along the way. Some players advance slowly, others take strange side paths, but all advance."
In Steambirds some of the elements of the Arrow of Play is Inevitable Decay (plane health almost always go down), Escalation (enemies get more plentiful over time) and Resource Flow (completed goals earn you copper which help you complete more goals or unlock new missions)
One often seen elements of the Arrow of Play in roguelikes is the Food Clock (you need to advance in your search of food else you die), but besides that there is little in terms of game play mechanics that actually drive you forward in a roguelike. On the contrary a lot of roguelikes leave most of the choice of when to progress further in the hands of the player. In roguelikes with respawns or non persistent maps a player can continuously scum a few levels to build a very strong character and only when confident enough that the next level can be handled the player delve deeper. I'd like to see more game play elements in roguelikes that constantly push the player forward, keeping the player on the edge of his capacity. Levels could decay or become increasingly lethal to stay on to prevent level scumming or the player could be hunted downwards by some always highly out of depth monster or arch nemesis. Only when the player has gone deep enough and become strong enough he has a chance to stay and slay the hunting enemy.