Any good guidebook will tell you that there are several alternatives to doing Milford Sound, from walking the Track to flightseeing, taking a cruise, and taking in Milford from Te Anau on a bus. My recommendation is that if you have time and money, you will try to do all of them, for Milford Sound is surely a miracle of nature, and because it is not easy to get to from the states, once there, you should stay as long as you can and take advantage of everything that is available.
I am not sure that my skills are up to snuff to allow me to describe Milford Sound. Suffice it to say that my experience was unforgettable. Being short on time, we chose the two fastest alternatives--flight seeing from Queenstown and cruising Milford Sound. Prior, we had heard that the Milford Sound area can be very wet, and that frequent windy conditions sometimes make flightseeing inadvisable. However, we were just blessed with the most perfect weather imaginable: it was a cloudless day, the sky was a deep blue, and the sun's spectacular appearance was just magical.
The flight took us over the Milford Track, with views of majestic, snow covered mountains, where small waterfalls were the only reminder that spring had arrived. Of course, the flight also goes over the amazing Sutherland Falls and Lake Quill. The pilot navigated fairly close to the mountains, and sometimes you can just imagine the wings of the plane touching the two ranges on both sides. Suddenly, the mountains turned color--if you can imagine that--and all I remembered of our approach to Milford Sound was how green, and gleaming it all was. The mountains were blanketed with a green color, while the water was, what else, green. Contrast this with the deep blue sky, and the vista can not be any more beautiful.