When talking 1990-91 hockey sets, there's all kinds of bad to talk about, and today we see both ends of the spectrrum.
1990-91 Pro Set was the set so bad for quality control (just glance at all the errors which made it through to the final product), that over time it became good to collect for many, including me. The set design is distinct, and the errors just give something to collect even if you have the massive set - over 700 cards. It may be overly produced, and you can probably still find packs or boxes for relatively low prices, even with the recent boom.
Definitely one of my favourite - so bad it's good - sets. What are yours?