went on a day trip from leeds a few years ago, thought it was lovely, really quaint. keep an eye out in the minster for the plaque to the soldier who died falling off his horse in the phoenix park. the minster is really impressive and it's all just so olde worlde, some great old style pubs too.
I spent a few days there about 10 years ago and enjoyed the history of the place - Yorvik (the Viking exhibition) is great, as was the Railway Museum, York Minster and the various ruins dotted around the city walls. Enjoyed a river cruise too.
I do remember that the city "closed down" at 5.30 - 6pm, very little to do (other than restaurant/pub) - no late night shopping for instance - but it was 10 years ago so maybe it's changed.