As a (former?) Marriott member, I was keen to try my first St Regis experience at this property, and overall, was very impressed.
First, the minor annoyance: Unlike other Marriott users here, I often get upgraded to a suite, and am generally pleased with the upgrades. However, they refused to upgrade me to a suite, as they said their 'Shenzhen suites' were all booked out, and their premium duplex suites were not upgradeable as a platinum benefit. Was quite disappointed with that.
However, everything else was great. The room decor and size was incredible. A real cut above. The service was fantastic. Buffet breakfast was great. There's no lounge, but the platinum 'happy hour' is basically like a lounge (for that limited amount of time) - great free food, free drinks including prosecco.
The pool and gym is fantastic, with incredible views (as you'd expect being on the 75th floor!). The spa was good.
The hotel was conveniently located close to the HK border, and is directly above a metro station, which means you can head into the city centre.
We also ate in the restaurant on the 99th floor. Expensive, but excellent quality.
Would definitely return to this hotel, and keen to try out more St Regis hotels