I just made an ADR for Biergarten for our trip next week. They had plenty of times still available (unlike most of the other WS restaurants).
I have to admit that this is the ADR I am most not looking forward to. We've eaten there a couple of times before and our kids always love the show (which is great), but I never really enjoy the food. (I guess I don't like German dishes in general, so maybe it's great food but just not for me). When I eat at Disney I look for a great theme and also great food and I just haven't had the great food part at Biergarten.
All that being said, I still made the ADR and our kids will have a blast and my husband & I will drink beer to "ticky tocky, ticky tocky, oy-oy-oy!" I guess in the end the mediocre food will be okay because of the rest of the experience.
So, I say it's worth it to go at least once. The show and atmosphere are great!