We blew through in about ten minutes. It is very small, and to us as 'locals' didn't have a lot of appeal. The Alaskan State Museum in Juneau is much more interesting historically, while Tongass seems to be more about recent history and the local industries like fishing and logging. It was ok, but there were a couple of old broken displays that should have been removed, and I just didn't get the feeling that the staff were really trying because of it.
Ketchikan is a really interesting place, and personally I learned a lot more by visiting Creek Street, and just taking the time to stroll around town a little and absorb the sights than looking at old fishing and logging gear in a glass display.
This review is the subjective opinion of a TripAdvisor member and not of TripAdvisor LLC.