This is one of my favorite films. How was the workprint different?
Well, not that much is known about it to be honest. The IMDB says that test audiences were 'unhappy' with the film. But there really doesn't seem anything to back that up. What is known is that John McTiernan made his version, submitted it and waited for approval. However, Micheal Crichton decided he didn't like it, so he went ahead and re-cast a lot of the parts and re-shot most of the film, which is why it was delayed for 15 months.
The film is then an odd mix of McTiernan's version and Crichtons. You can tell it's messed up because not only are their styles completely different but the actors have gained/lost weight.
Anyway, there's little chance of this ever seeing the light of day. As far as I can tell, the only time the original footage was seen was during the initial test screenings.