I visited 4 of this serial site locations in August-September of 2023 on a self-driven tour around Sardinia, in addition to the already inscribed Su Nuraxi di Barumini.
Santu Antine was one nuraghe that I would call the most impressive, even more so than Su Nuraxi. Unlike the latter, Santu Antine's defined interior spaces actually allow proper exploration of the main structure, including several fairly walkable covered passages. It is hard to imagine that it would be overlooked for inclusion when and if the decision to extend comes along. It is also more photogenic, IMHO.
Palmavera is significantly more compact in its core, but its outer precincts are not far behind those at Su Nuraxi. There are a couple of uncommon surviving artifacts on the grounds, such as a sandstone nuraghe "model" on a circular altar and a stone chief's seat. Depending on how many locations are selected to be included on the extension list, it is questionable if it will make the cut.
Parco Archeologico Santa Cristina is a larger nuraghe+. Its central part is well-preserved remnants of a Christian village, centered on the church built on this site around 1200 CE. The nuraghe proper is located in a surprisingly wooded area a couple of hundred meters beyond the village. The central fortress here consists of a single truncated tower, while the rest has more of a feel of an archaeological dig, with only a few defined structure outlines. There is another roofed space that can be entered, however - a "barn".
Separated from the nuraghe by the aforementioned village - about half a kilometer away - is the sacred well temple; the triangular chiseled opening in the ground is clearly the killer feature of the park. I don't think the nuraghe is representative enough for the inclusion on the WH extension, but the well may further its case.
Finally, Sant'Anastasia is technically just a small archaeological site excavated around an 11th-century church. There is no nuraghe fortress/tower here. On maps, the place is called <em>Pozzo Sacro di Sant'Anastasia</em> - the sacred well - because its key feature beyond the church is also the Nuragic well temple, smaller, more ancient-looking, and with surprisingly a larger water reservoir than its counterpart at Santa Cristina. I doubt that Sant'Anastasia will make it on the final list of the WH extension, but I do know many other serial site locations that feel unworthy, so who knows.
We picked these sites due to their proximity to either our bases in Sardinia or our driving routes. Each requires between thirty minutes and an hour to see. There are no good public transportation options to reach them, so driving is required. At all these sites, guided tour options exist, but you can explore on your own, with the information provided either via a phone app, a booklet, a set of information stands, or sometimes by the otherwise unoccupied attendant.