Groningen is a nice (partially) old traditional town with all the facilities of a big city. Within the town center almost everything is within walking distance; being a 40% student town, this includes hundreds (yes hundreds) of bars and pubs and about 12 dutch coffee shops. the only main problem with Groningen is that it is slightly segregated from the rest of Holland, there is a lot of nothing within 1 hours train or car trip (which is quite far for Dutch standards). Groningen - Amsterdam is about 2 hours by train. Grunn is a very friendly town and is often nominated to be and won the title; safest town in Holland. Like the rest of Holland, the best time to visit is during the summer when people are warm and friendly and the town is alive.
I visited the city various times when I was in the Netherlands in 1988-89, and it was a very enjoyable experience. It is a very nice city.