You also get a discount with Disney Club (50% off). I was disappointed in it, but I think it was primarily due to our guide (Vincent). He was VERY boring, and about half our group left before the halfway point. Another thing that disappointed me about it was, like MissScarlet, we knew almost everything he said. There were a couple of things that we didn't know, but I really expected the tour to discuss things that can't be found in books. We did the tour because we have been to
Disneyland a lot and wanted to do something different, and wanted to find out more "behind the scenes" kind of info.
I would do it again, but I would avoid Vincent. (There were 2 guides for our time slot, and we just split into 2 groups.) It does take quite a bit of time though, about 2 1/2 hours. Our tour sounds different from MissScarlet. We did not go on the Mark Twain. We also ended at the Disney Gallery (another disappointment...it was closed, and Vincent did not know that, even though there was a big sign in the front as well as the back door where we were). He offered to take us on the Haunted Mansion with him, but no one took him up on his offer.
I agree with MissScarlet...do it only if you have the time (we stayed there 4 days). It will probably be especially interesting to you if you don't know a lot of the details behind Disneyland. My only additional comment is, again, avoid Vincent. (He's a very tall, lean guy with dark hair and glasses. I think he had a small moustache too.)
(As a side note: we went on a tour of the Grand Californian, where we were staying, and really enjoyed that one. It's free, about an hour long. Not sure if you need to be a guest or not.)