Wikipedia page for it is not only not informative and very short, but it was almost certainly written by either the winery whose bottle is shown in the picture or by some other kind of PR organization with a pretty shaky grasp on the English language. The entry in the Oxford Companion to Wine isn't much better (though, as you might expect, their English is impeccable). They tell us that the grape is grown on about 5,000 hectares of land around the city of León in northwestern Spain. Further, the grape is "unusual," "musky," and "light in color but very distinctive." It is permitted for use in the Tierra de León, Valles de Benavente, Valtiendas DO regions, but a good deal of the production is bottled under the Vino de la Tierra Castilla y León heading, which is essentially the Spanish equivalent to a Vin de Pays in France or an IGT in Italy. Why much of the wine is relegated to this lower quality rung is a question that isn't explored or answered.
Aside from that, there isn't much to say. A comment left on the VINEgeek site informs us that the word Prieto means "dark," referring to the fact that it is a dark-skinned grape, and Picudo means "peaked," which refers to the sharp taper at the bottom of the bunches. The always excellent Catavino adds that the grape is thought to be native to the León region of Spain and there are at least two clonal variants of Prieto Picudo: one with oval-shaped berries and one with round berries with the latter type being preferred for wine-making. Interestingly, that post from Catavino is from 2005 and the writer there seems pretty excited about the possibilities for Prieto Picudo given the wines that he tasted. In 2010, a different writer for Catavino was much less enthusiastic, saying in reference to six different Prieto Picudo based wines that he had recently tried: "To just about anyone, they were awful." To be clear, he wasn't slamming Prieto Picudo as a varietal, as he does say later in the pieces that he has had some good examples. His concern is more with the wineries, or at least the wineries represented in this particular tasting, and their improper treatment of the grape once it leaves the vine. Without knowing exactly which wines he tasted and exactly what their sin was, it's hard to come a judgement of one's own, though.
Marty's in Newton) within the last year, but, weirdly, they had two different examples. The one that I bought was the 2006 Dominio Dostares "Estay" from Castilla Y León, and I paid about $16 for it. In the glass the wine was a fairly deep purple ruby color that was nearly opaque at the core. The nose was moderately aromatic with red cherry, strawberry and red berry fruit along with some baking spice, chocolate and smoke. On the palate the wine was medium bodied with medium acidity and low tannins. There were flavors of red cherries and both stewed and fresh, brambly red berry fruit (as an aside, the tasting note "red berry fruit" makes me a little uncomfortable as I try to be as precise as I can, but sometimes I just have a vague sense of fruit that is red and berryish which doesn't announce its presence in a more assertive way, so "red berry fruit" it is). There was also a touch of baking spice and a kind of cedar-y woodiness as well. As it opened up, it picked up something that I've never really been able to put a name to, but which is always unwelcome in my glass. The closest I can come to describing it is that it tastes kind of like the strawberry flavor of those awful candies that Life Savers makes called Creme Savers. In my notes I write "strawberries and cream," but it's that artificial kind of cream that those candies had (or, similarly, like the artificial cream flavor in Cream Soda soft drinks). I've picked it up in red wines made from a variety of grapes, so I'm guessing it's something that happens during the winemaking process, but when it shows up, it's a total deal-breaker for me. This wine wasn't the worst offender that I've ever tasted, but that flavor was there. I'm willing to try another example of wine made from this grape from another producer, but I probably won't go out of my way to seek one out or pick one up.