Capt.Redblade has it right - the range has such pulling power and offers so much enjoyment to kids and AFOLs that, if handled properly, means it should run and run. I ended my dark age with Batman I, and now see my kids loving Superheroes as much as I do and using their box of bricks to make random scenes and bases like we used to when the closest you got to a Batman figure was a guy with a black helmet and a bad-hand painted badge.
The range is strong on its own, and has support from other ranges. The cross-over with City is effective - even if it is only to provide a supporting cast/ victims/ scenery to the adventures of caped heroes and sinister villains. And what could be a better bit of scenery than the modular town hall (for those lucky enough to afford it, while we others can just imagine how cool the Joker would look in the mayor's office as Bats lands on the roof). Equally the expansion of the range across prices and complexities of build is impressive, and would suggest that TLG learnt the lesson of Batman I. Allowing kids to buy a jet ski with Batman for a few dollars in the US or get hold of it through an iffy paper in the UK, and then producing a pretty inspired Arkham at the opposite end of the scale while filling the gap between those 2 extremes with various iconic vehicles and scenes caters for a huge range of fans, with a huge range of ages, wallet- sizes and space.
Bring on Wayne Manor as the next exclusive, I say. Although the haunted house has potential....