As simple as it sounds, this feature may be a stroke of accidental genius. I say accidental, because it's an idea that evolved largely in single-player, as a way of offering a controlled yet non-linear path through the levels. But in multiplayer, where the frontline is pushed back and forth as the two teams tussle for control of the map, the frontline device solves one of the biggest problems of the Battlefield series.
The problem is this. In Battlefield, you generally have to control a number of points that are strewn across the map, which means your forces need to be split between those defending your existing points and those attacking new ones. In practice, what this usually means is chaos, because nobody wants to defend and everyone has different ideas about which point to attack next.
Frontlines banishes that chaos. Here, everyone is fighting along a single, focused front. Defending and attacking become virtually synonymous, and nobody is left roving the wastelands wondering where the action is. For this reason alone, Frontlines has the potential to be more fun than vanilla Battlefield ever was.