I thibk, upon first introduction, Poseidon could be viewed as a God of indecisiveness. He is not entirely one way or another. The sea can be both terrible and calm, horses wild and tame.
This may be why He is so under-worshipped. Most people, in modern times, are one way or another. Or perhaps clear on what they are striving to be.
I see Poseidon as a God for those seeking guidance in coming to terms with their inherent duality.
This post is brought to you by insomnia and severe disappointment with the election results. No surprise that my Lord and Tamera of Tumultuous Seas is on my mind tonight.