Opportunistic routing is a well-known technique that exploits the broadcast nature of wireless transmissions and path diversity to form the route in an adaptive manner based on current channel conditions. This paper studies the throughput advantages of opportunistic routing over conventional multihop routing for linear multihop wireless networks with type-I Hybrid Automatic Repeat reQuest (HARQ) and quasi-static Rayleigh fading channels. The end-to-end throughput of opportunistic routing is derived using Markov chain tools and accounting for fading statistics. Both fixed-rate and optimal-rate transmissions are considered. Moreover, an investigation of the throughput using standard information-theoretic performance metrics for asymptotic signal-to-noise ratio regimes is provided. Specifically, the multiplexing gain and energy efficiency (i.e., minimum energy per bit) of both opportunistic and multihop routing are analyzed. Numerical results are given to corroborate the analysis.