Cagliari and its port just have a good feel to them. What more is there to say? There are daily…read moreferries operated by Tirrenia and other lines going to all sorts of places, including Civitavecchia (port for Rome), Naples, Palermo, Genova, and even Tunis! There are also cruise ships calling on Cagliari from time to time, including some of the well known ocean liners.
The naturally air conditioned summer evenings make it an ideal place to stroll, eat a gelato, people watch, or some combination of all of these things. The atmosphere is relaxed. Naples it is not.
The only reason I'm deducting a star is because the area does not really hold any noteworthy hotels, though they are decent. There is one very good hotel at the east end of the port where Via Roma sort of makes a bend and merges with other major streets as it heads toward Il Poetto, but I don't remember that hotel's name.
At any rate, Cagliari is essentially a very pleasant city in a beautiful setting and with a laid back vibe. You won't need a vacation from your vacation in Sardinia. Not a chance.