Different opportunistic routing protocols have been proposed recently for routing in sensor networks. These protocols exploit the redundancy among nodes by using a node that is available for routing at the time of packet transmission. This mitigates the effect of varying channel conditions and duty cycling of nodes that make static selection of routes not viable. However, there is a downside as each hop may provide extremely small progress towards the destination or the signaling overhead for selecting the forwarding node may be too large. In this paper, we provide a systematic performance evaluation, taking into account different node densities, channel qualities and traffic rates to identify the cases when opportunistic routing makes sense. The metrics we use are power consumption at the nodes, average delay suffered by packets and goodput of the protocol. Our baseline for comparison is geographic routing with nodes being duty cycled to conserve energy. The paper also identifies optimal operation points for opportunistic routing that minimizes the power consumption at nodes.