Lamb shoulder needs moist heat to make it tender. It's usually braised or cut up for lovely stews and pilafs and curries. I am envious that you can find it; here it's not always available, because many stores only buy the hindquarters.

But, it is not tender like the leg. I have seen roasts, but in English cookbooks, where I think they must have younger lamb.
The rotisserie might just work. More likely that than roasting in the oven.

I find lamb shoulder very tender...easily as tender as the leg...if it's really young spring lamb and not 1/2 way to mutton.
I would grill it...cook it medium rare, season with garlic and baste with lemon...
Linda C

Here in Australia, the land of the sheep, I was brought up on a diet of lamb in its various forms, and it was rare that we had beef.

I always roast lamb in the oven - and put a container of water in the oven with it to keep it moist. Lamb should never be entirely trimmed of fat - it's the fat which keeps the meat moist and tender during cooking. The container of water sort of helps these days when lean meats are the Go. That means, of course, that a rotisserie, where the fat drips off, won't result in moist and tender. IMO, anyway.

The shoulder CAN be tougher than the leg, because it's those shoulder muscles which are used more when the lamb is walking. However, properly cooked, and young enough, it is quite a good cut of meat. If it's been marinated, it should be very tender, and faster to cook.

It's a pity you couldn't un-net it, then cover it with stuffing (I use the same stuffing as I use for chicken - bread, onion, mixed herbs) then roll it up again. Boneless shoulder is delicious done this way.

Christine, I think it should be okay for dry heat cooking. I noticed that most of the recipes for lamb shoulder are for braises but my butcher assures me that this can be dry roasted. The shoulder chops from him are tender when grilled.

Lamb leg would isn't an option for us as we keep kosher - the hind quarter needs extra work to be kosher - the sciatic nerve and fat around it has to be removed. I've heard it is available in Israel but I don't think there is a source in the US - they just prepare the front to sell as kosher meat and sell the hind quarters elsewhere.

Linda, it was marinated with sort Mediterranean flavors - cumin, coriander, rosemary, a bit of thyme, garlic, black pepper, balsamic vinegar, olive oil. I meant to stick some more garlic cloves in just before roasting, but I forgot.

Daisy, This looks like it has a reasonable amount of fat. Cooking on gas should help with moisture because the combustion produces some water vapor as a by product. That's why gas ovens are suppose to be ideal for breads and roasts. I'm putting some rosemary and thyme cuttings on the fire too. Rotisserie cooking is generally very good for keeping meat moist and tender. The turning self-bastes so none of the meat dries out. It certainly works that way for the chickens and turkeys I've cooked. I could have un-netted and stuffed it, but I really didn't have time.

I started out without a pan to catch the drippings but I had to much flame up so I've put a pan in. I put some water in it too so the first drippings don't burn before they get more to join them.

I'm committed now. We'll see how it comes out.

Funny, Gardenweb can't seem to count. It said this thread had one followup when Christine and Linda had replied - now that Daisy has replied it says 2 replies instead of 3.

I am with you Cloud Swift and LindaC. We use shoulder lamb roasts since our son is allergic to beef. I have roasted it over charcoal in the Weber Kettle and in my gas oven. It has never been dry, quite the contrary. Lamb shoulder roasts have ample fat and are always moist and tender in my experience. Your seasonings sound wonderful. Let us know how it came out.

It came out tender enough. I think I should have had the flame up a bit higher as the outside wasn't quite as crusty as I would have liked. Also, I think next time I might open it up to put some spices inside even if I don't stuff it and pat some on the outside after the marinade (like a rub) as the marinade spices were pretty subtle.

Marinated meats won't get real crusty on the outside. When you want that crisp, seared outside you want the meat to be dry. It helps to blot the meat with a paper towel before searing to get a really nice sear on it. You could skip the marinade altogether, push some cloves of garlic and sprigs of rosemary inside the roast and rub all over with those herbs you mentioned, or try Zataar as a rub.