We've been to Interlaken several times, staying in different places each time. This was the best experience by far - although the fabulous weather all week may have biased us.
We got a very warm welcome at the registration desk, special "passport" for our younger child, and smiles from people in the breakfast room every morning who got to know our faces.
This old hotel did not seem old on the inside - it was in very good shape. Our rooms (a pair connected by a door) were large, luxurious, and the bathrooms were very modern. We had robes of different size thoughtfully provided for each member of the family. Fruit and chocolate each day. There were not a lot of children (more on the weekend), but those that were around were well-behaved and ours certainly felt welcome. During this very warm week, we were initially surprised to learn there was no air conditioning, but we found opening the windows worked fine and was refreshing. The air was great and there were no bugs. We never felt the room was too hot. The pool with outdoor saltwater jacuzzis was fabulous. The main pool would occasionally get a little crowded with lap swimmers, but the congestion would generally resolve within 10 minutes and was surprisingly empty most of the time.
We found the service to be outstanding overall. On the day we left, the doorman handed us each a bottle of cold water and gave as a very warm sendoff. We had a great time and would have no hesitation in returning, even at the admittedly pricey rates and unfavorable current exchange rate.