As the name implies, Bluetooth Low Energy (BLE) is built specifically to consume small amounts of energy and make phone batteries last longer. But there are limitations with BLE when it comes to transferring data. BLE only supports very low data rates and you cannot stream audio using BLE.
Why it might be a NFC killer?
iBeacon(BLE from Apple) could be a NFC killer because of its range. NFC tags are pretty cheap compared to NFC chips, but NFC tags are required on each product because NFC works only in very close proximity. In theory, NFC range is up to 20cm (7.87 inches), but the actual optimal range is less than 4cm (1.57 inches). Also, mobile devices need to contain a NFC chip that can handle any NFC communications. On the other hand, iBeacons are a little expensive compared to NFC chips, but iBeacons range is up to 50 meters. Not all phones have NFC chips, but almost all have Bluetooth capability.