I think each routing protocol has some objectives that makes it special comparing  with other routing protocols ,

but generally we can say that the common primary objective is to save battery energy . Hence , energy efficiency is the main purpose of most routing protocols.

Furthermore, QoS support in terms of network throughput, end-to-end latency and data delivery ratio is an important objective for routing protocols

primary objectives of the wireless sensor design are balancing network energy consumption and extending the entire network lifetime. The analyses the effectiveness of LEACH protocol in cluster-head selection, and proposes an improved clustering algorithm. This new algorithm takes nodes residual energy and location information into account, optimizes the selection method of the threshold for electing cluster-head, improves optimal cluster-head selection strategy that is normal nodes select the optimal cluster-head based on the cost function. 

Thank you Dr.

in addition, the new algorithm will take also the security issue into account , right?

I think each routing protocol has some objectives that makes it special comparing  with other routing protocols ,

but generally we can say that the common primary objective is to save battery energy . Hence , energy efficiency is the main purpose of most routing protocols.

Furthermore, QoS support in terms of network throughput, end-to-end latency and data delivery ratio is an important objective for routing protocols

sensor networks are used to to monitor and sense "physical" parameters or environmental conditions such as temperature, pressure, ground humidity, prediction of earthquakes by sensor the sound, then cooperatively routing protocols used to forward their data through the network to a central computer .

the primary objectives of routing protocols are conserving network energy and increasing life time of network

Thank you Majd, Huda and Ahmed 

Primary Objective of WSN routing protocols are Power consumption, reliability and Congestion control.

Primary objective of any routing protocol is of finding best path, but in case WSN it is still best path but also energy efficiency. other then that scalability, Data aggregation, Network life time,fault tolerance latency, deployment, Quality of service. these can also be considered for designing the Routing protocols.