Brown Derby had them last April, and they were succulent and delicious. In fact, our server said they'd be the best I'd ever eat. Well, he wasn't quite right as I've had them numerous times in my life, but they were quite good. And if memory serves me correctly, I believe they come with the traditional mint chutney/sauce. Mmmmm, making my mouth water and it's only 9:30 in the morning. . .
Jiko serves a lamb shank and my bf ordered it when we visited in September. The presentation was quite frankly repulsive. So much so in fact that we had to request that it be removed from the table. It was a giant hunk of meat still attached to the bone. The end of the bone was jagged, like it had just been torn from an animal's mouth. My bf tried the lamb and said that it tasted good, but he could not bear the sight of it. By the way, he is French and the French are generally much more tolerant of unusual food and "carnal" presentation than we Americans. To Jiko's credit, the waiter removed the lamb from our bill.
Overall, Jiko was the only disappointment during our WDW trip that included visits to California Grill, O'Hanas, Brown Derby, Spoodles, Marrakesh, and Le Cellier. I was unhappy with the bland halibut that I ordered at Jiko. It was especially disappointing because I was really looking forward to trying Jiko and the restaurant is beautiful.
I've had lamb at Citricos (actually a lamb sirloin, I believe, and it was good) and at Brown Derby (rack of lamb, also good, but service was below par). However, the best lamb chops/rack of lamb I've had anywhere (not just at WDW) was the rack of lamb at Portobello Yacht Club in Downtown Disney. We'll be returning the first week of January, and I already know what I'll be having as my entree.