Main features of tour (Milford Sound Cruise, TransAlpine train ride,etc) were very enjoyable and impressive. Guides were mostly very informative and sometimes funny. Free day in Queenstown was great. But...I guess we are not really guided tour people. We enjoyed not having to drive ourselves but we would have liked the flexibility of doing our own thing.. I guess we should have kept the rental car after all. For example it was pouring as we headed for Mt. Cook.. Could not see mountain at all and could not go walking as we had planned. If we were on our own we would have skipped Mt. Cook and just headed for Queenstown. That would have gotten us in much earlier.
That reminds me: One of my biggest complaints was that the first 2 days were really long driving days - about 12 hours on the road. Maybe you should consider having people stay in Te Anu as a starting point for Milford Sound. It is lots closer,