As with many other reviewers here we visited only Hovgarden, which proved to be an enjoyable out of the way idyll, even if the actual remains weren't especially spectacular.
After a quick free trip on the car ferry we headed to the site. Just in front of us was a guide in Viking dress conducting a tour in Swedish, we were too far away to hear anything, but it did highlight to us the route we should take around the grassy mounds. There were a few small boards dotted around to help interpret the green lumps and stones in front of us, but to be honest there wasn't really much to grab me. It was a nice stroll, especially when we got down to the waterfront and found there was a little boat going over to Birka, however the cost and amount of time required for the return boat quickly ruled it out.
It was a pleasant and idyllic way to spend a morning in the warm sunshine, however I don't feel that I really got much understanding of the value of the site. A trip over to Birka and its museum could hopefully provide a more thorough explanation however the large cost in terms of both money and time rather put us off making a visit. So we didn't see the best of the site but we had a nice morning, and the route back to Stockholm goes straight past Drottningholm so we had an enjoyable stroll around the gardens there to round out the visit.