Our room in the Don Manuel was small, clean and outrageously noisy in the early morning hours of a festival weekend. That said, the location is excellent---a long fly ball to the Atlantic through a myriad of interesting little streets and squares.
Gijon itself is wonderful, and the Don Manuel would be a good and economical choice for a single person in town for a couple of week-nights. But that's about it. The rooms are uncomfortably small for two people, and I wouldn't dream of staying here on a weekend. (Try the more expensive parador instead.) The discos don't get going until 2 a.m., and they don't seem to close until 5---whereupon the street beneath your window is flooded with blitzed revelers. I suppose you could close the windows, but then the room would be stuffy, so it's an unpleasant choice to have to make.
Still, the only complaint I have about the hotel itself concerns the outdoor restaurant. The service is glacial---at best. (Mostly, it's just non-existent.) You could sit there for an hour or more without being served---or, indeed, ever seeing a/the waitress. I walked out twice.