It's awesome. Did it on the weekend. Stopped at Cwm Rhaeadr first, 4.5 mile loop, really good fun. Then drove on to Brechfa for the Gorlech, trail is really good. Bit more black than red though I would say? Compared to Afan anyway! Came off on the 2nd downhil, black eye etc. Spoiled the rest of my ride really but will go back as the trail is great fun.
Just a quick note to the OP - if you're looking for interesting Blues then also look at Verderers in the Forest of Dean - about the same distance for you in the opposite direction to Brechfa . Went there for the first time yesterday and had an absolute blast. The Verderers trail is actually very similar in style to the Derwen blue and greens, though the surface is less "groomed" (more rocky and natural seeming), and the descents and jumpy bits even more flowy and fast (actually felt the benefit of "pumping" the trail for the first time).
were you with the HWU lot? so was i