Orkney has some nice archeology, a few World War features, Italian chapel and a few barriers, and the obligatory snap next to the sign pointing towards the hamlet called t**t! But other than that I found it a little dull. The old street is Stromness is picturesque but I personally wouldn't make a special trip to visit. We went there for a week scuba diving the wrecks in the flow, and had a day doing tourist stuff when the weather meant we could not dive, but I'm not sure I'd return.
I suppose it depends on whether you intend visiting the north coast again soon?
Do visit the caves at Durness. The drive along the north coast is nice (I say drive, I have traveled that road three times, but only by bicycle).
Perhaps there are things to do on Orkney which I missed and others will tell us about?
Edit: apologies to the mods, if this post is flagged for rude language. The hamlet really is called T w a t.