This site is highly underrated in my opinion. As many people, we only went to Nazca to take a flight over the lines. However, as we had a few more hours until our bus, we looked for other things to do in Nazca. We did not expect much but found the cemetery (and the Cantalloc Aqueducts, which are usually done together in tours) fascinating and were surprised to be almost the only tourists there, in high season. A similar site in Europe would probably be filled with tourists.
The cemetery itself takes less than an hour to visit but is a bit far away from the Nazca city center by car, and requires to go through a long gravel road. It is recommended to take a tour as there won't be any taxi there to bring you back. It takes less than an hour to visit, but count another one hour and a half of car to go there and come back to Nazca (if this is too long for your schedule, the aqueduct is probably a better choice as it is closer and a bit more unique).
The airline arranged our tour with a local guide, but it is really easy to find a guide in Nazca. They initially asked for 80 soles per person for a 3-4 hours tour for four persons (incl. the Aqueduct, the cemetery and a few other sights on the way) but we negotiated the price down to 50 soles per person. The tours usually don't include the entry tickets of the Aqueduct (10 soles per person) and of the cemetery (8 soles per person) that you can buy at the entrance.