What disappoints me is when only the first season is released. And when you are missing part of a story because of a crossover episode.
I was pleasantly surprised by The Bionic Woman which came with cross over episodes from The Six Million Dollar Man.
I was unpleasantly surprised when the audio went out on a second season episode of the The Bionic Woman.
I had to buy a couple of seasons of Hercules to get the crossovers from Xena of the Hope and Callisto arcs. I ripped them and made my own compilation DVDs with everything in order.