He will be good (maybe not great) this season and we should likely be even better than last year. With the cap rising again next year, we should be able to move him and receive assets in return if that's what Danny chooses.
Horford isn't as sexy as Durant, but we still got the 2nd best available free agent this offseason without giving up anything to get him. It is an exciting time to be a Celtics fan - don't let the super-wuss Durant get you down!