Menca makes my list of what I consider Spain's four 'truly great' red grape varieties, with tempranillo, garnacha and monastrell. (Then there are a few others which can reach greatness in very specific terroirs and climates.) It has excellent structure, a funky/fruity combination in aromas and flavors that gives it a somewhat wild attractiveness, plus a marked ability to pick up the terroir - usually schist in Bierzo and in Ribeira Sacra. I believe its aging capability, when sourced from low-yield vineyards, is undeniable. On the minus, or at least 'warning-sign' side, I've noted a tendency by menca, which has a high natural pH, to be infected by Brettanomyces rather often. Winemaking cleanliness recommended!
I've just finished an hour ago (coincidence!) one of elmundovino's weekly (blind, of course) tastings, this one devoted to Galician reds from several appellations (Valdeorras, Ribeira Sacra, Monterrei, Ribeiro and Ras Baixas). The best wine in the tasting, easily, was a thoroughly mindboggling Ribeira Sacra menca, Gumaro B1P 2007, made by young Pedro Rodrguez (with 20% of the stems on, by the way). All the concentration and power of a Bierzo menca, plus - amazingly, for these features seem incompatible - all the freshness and elegance of Ribeira Sacra. Delicious stuff, and it bore its oak effortlessly - it hardly showed, but it'll help the wine develop. It'll be interesting to see its progression. This is a wine that Cte-de-Nuits lovers will appreciate.