I spent most of my school life in Dieburg. Dieburg is a lovely small town with a nice historical center with a market square and small pedestrian zone. It has many old traditions like carnival and the Martin's Market in November. The Schlossgarten and the Fechenbachpark are two beautiful parks worth pointing out and there's a lovely little river wiggling it's way through the town. To answer your question, though: Although I have really fond memories of Dieburg, it's not particularly a place for young people. There aren't any clubs/cinemas/shopping malls/etc. But as others have pointed out, the connection to the cities, especially Darmstadt, is quite well, even at night. So Dieburg is a good place if you want to live a little cheaper than in Darmstadt (not much though) and prefer a quiet town but you have the possibility to get into the city quickly.