Hi,
Metz is an old historical town, the main town in Lorraine. I've spent over a week there visiting the place one time. If you want to see historical evidence, see the ramparts. The city was fought over three times, 1870, 1918, 1944. Culturally, the cathedral is worth seeing.
Great that you have a rental car if you want to see more battlefield sites, war museums and cemeteries around Metz....Gravalotte, St Privat, Mars-la-Tour. I took the bus from Metz and had to walk back 5 miles back to the next town from Gravalotte.
War cemeteries dot the edges of these villages en route to Metz. I saw them in 1984 en route to Metz.