Hmmm-. We spent a few nights here on our honeymoon. Although we had a lovely time,we were happy to have only stayed the few nights. The town Porto Cervo itself was built in the 60s, so is not the old traditional Italian town you might expect. Super yachts yes, big brands yes, but it lacks the charm of old Port towns gone fancy such as St. Tropez.
The hotel itself is ideally located next to Vuitton and all the other brands you might expect. The pool is so so, their private beach is a 15 minute shuttle ride away and is lovely. The staff are wonderful, but the hotel is a little 'tired' and outdated. Stay here for a lovely quick in and out stay, but for a longer stay opt for a resort outside of town for better value (still very expensive).
The water is where it is at. If you don't book a boat, dinghy, or a canoe (lol!)- you are missing out of the Costa Smeralda's entire raison d'être. If I were rich enough I would sail in on my yacht, enjoy the waters for a few days, only go into town for a nice bite and cocktail and then zip staright back to my private floating home to move on.