Say what you will about Mike Love, but Kokomo is an undeniable hit that achieved its iconic status organically because people heard it and liked it. It's also full of beautiful little musical touches (the combination of tinkling steel drums, accordion (played by Van Dyke Parks), and dobro (played by Ry Cooder!)
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And I agree, "Kokomo" is a very good, catchy little pop song. No, it's not earth-shattering but neither is it anything to be ashamed of. "Somewhere near Japan" is more interesting to me and has more substance but I guess they did that song because of the "exotic"-sounds-formula "Kokomo" had established and rather than for anything else. But what a great record it is.