Though it's not mentioned in Epson's own literature, but is somewhat vaguely mentioned in one seller's listing, it appears that the Hot Press and Cold Press papers are actually two-sided, as my front-and-back test prints seem to indicate. That said, they still labeled the Velvet Fine Art the opposite of the glossy paper types.
Luminous Landscape has a review of the papers by Mark Dubovoy that's quite well written. Though I need to order more paper to be able to complete my tests, my initial reaction is as follows: The Hot Press papers are smooth, but the surface seems better to me than the overly deep (or high) texture of the Cold Press papers. The blacks are good with both, but the Velvet Fine art holds the ink more evenly, with excellent detail, and reaches a slightly deeper black than the Hot and Cold Press papers.
Dual Sided but with the condition "sheets" in the info I have. The spectral plots of the samples I got are identical for front and back. The bright versions have an FBA content between HM PhotoRag Bright White and Moab's Entrada Rag Bright White which is a high load. The texture of the Epson Cold Press Bright (heaviest FBA content) is closer to a regular pattern (almost like Canson's Mi-Teintes texture) than the Epson Cold Press Natural is. Do not consider them as two varieties of the same paper, they are not.
met vriendelijke groeten, Ernst Dinkla
spectral plots of +100 inkjet papers:http://www.pigment-print.com/spectralplots/spectrumviz_1.htm