Will you have a car? I believe I've read that getting to/from the HDDR can be challenging on Disney transportation.
Never been to HDDR personally. We did love Biergarten last February. I'd eat there again just for the apple strudel and vanilla sauce.
If your timing is good, you can walk outside and watch Illuminations. Let me say--I've seen Illuminations from a number of places around the Lagoon, but the view in front of Germany is the best. The globe is right there and you can feel the heat from the flames on the water.