Metz is stunning. I have been there twice and loved it both times. The town is very tourist friendly. There are signs pointing to the main attractions as well as an awesome multilingual tourist information center that has free city maps and cheap self paced walking tour booklets you can buy. The tourist information center is very easy to find as it is located right next to the cathedral.
The cathedral is awesome. It is known for having tons of stained glass, about 70,000 square feet of it! It is quite something to go inside this massive cathedral to see the light shining through the complex, detailed, colorful windows.
The outside of the Cathedral is also very impressive, even when they are doing some restoration and preservation.
Aside from the Cathedral, there is a lot to see in Metz.
There is a very picturesque Protestant church that appears to sit on an island because the river splits and goes around the church.
Both times I was here there were many swans in the river around the church.
The opera house gave us a surprise by having a huge garden in the front. This garden was not here the first time I was here and it seems that it is temporary. These kinds of little surprises and changes is what keeps Metz interesting every time you come back.
There are many other sites to see in Metz that you can find out about at the tourist center, but these are definitely the top sites I want to see again and again and again.