Cisco's firewall road-map has been interesting. They started with PIX and advanced the market with ASA. After acquiring SourceFire, they came up with Firepower services. Firepower services on ASA was offering a lot of security features and has helped to fill the feature gaps within ASA, but it was running as two separate instances. That is ASA and Firepower.
Cisco has came up with Firepower Threat Defense (FTD) ,which is a unified image of ASA and Firepower. It is designed to do what ASA and what Firepower can ,together with unified management. Cisco FTD is capable of offering traditional ASA services plus NGIPS features, URL Filtering ,Application visibility and control (AVC), Advance Malware Protection, ISE Integration, SSL Decryption ,Captive Portal ,Multi-Domain Management etc.
Cisco might put all its focus on FTD and eventually the traditional ASA OS might get retired. You can find more details about FTD and firepower services below.