I've been to Christmas markets in several European cities. While I think they're all great local traditions, giving people a place to gather and feel festive despite the dark cold weather, some feel pretty repetitive or redundant after a while: the same food, the same crafts, etc. Not so with Vienna's outstanding markets. I visited at least 5 on a single day last year, and I found each had a distinct feel, unique merchants, and interesting food. I don't even really enjoy shopping, but it made for a good part of a great day out, despite it being cold and snowing.
I wouldn't say the gluhwein was notably different, but I sampled several just to make sure.