Stayed three nights on a business trip. Room was clean. Bed and pillows were outstanding. HDTV set, but appeared to be largely non-HDTV channels many with lots of static. Wifi was good until all network connectivity was lost on my last night there (both wifi and ethernet). Didn't affect me too much, but a little bit of a pain. I didn't really have any staff interaction nor did I eat at the hotel so I can't comment on those.
Based on this stay, I would recommend a Hilton Garden Inn to others and it would be my first choice when staying in Frederick (helps that it is on my company's preferred list).