Basically the 887 is a souped up version of the 870, with a higher price tag to match the camo, hi-viz sites, and the added gimmick features such as the "Nitro" and the "Bone Collector" name tags attached. It is only available in 3" and 3 1/2" chamberings. I haven't personally shot one, but according to what I've heard they aren't any better or worse than an 870, just overpriced.
From what I've seen in the Blue Book of Gun Values, since the model was introduced in 2010, it's comparative used values are about the same as the 3 1/2" model 870, which isn't so good when considering the difference in the new gun price between the two models. If I were considering purchasing a used one, I'd negotiate for a price more in line with a used model 870 and if I were buying a new one, I'd try to get it for about the same price as a new 870 rather than the MSRP.
NRA LM, NAHC LM, Buckmasters LM, The Second Amendment Foundation, GOA, NAGR, Palmetto Gun Rights, , ASAdisabled sportsmens' alliance, EDH, and Proud SC redneck REBEL still flying the Stars and Bars!