Defense Grid 2 both succeeded and failed. The funding managed to get the minimum $250K, but didn't reach any other level, much less the $1M that would have funded a full Defense Grid 2. Instead, an eight level expansion to the original game will be released.
However, it seems that Defense Grid 2 will still be coming, albeit much later. According to the Kickstarter , “We’ll need to do extra work on our end to earn or raise the remaining funds in order to complete DG2, but when we do, you’ll still be a part of the team. Crossing $250,000 gets you DG:Containment this December, and DG2 when it is complete.”
So, donors will still be getting Defense Grid 2 when it's done, though it seems developer Hidden Path will have to find another funding source to do it.