Just spent 3 days in St. Petersburg with the "Chaine des Rotisseurs" .
I can recommand both Grand Hotel Europe and Hotel Corinthia Nevskij Palace (altough the Grand Europe is more central for shopping).
A special mention for Restaurant Podvorie, near the town of Pushkin (Summer palace): Great Typical Russian lunch in an old wooden isba, and for the brand new "Russian Vodkaroom Nº1" at 4 Konnogvardeisky Bd. Outstanding selection of vodkas, with a tasting bar, a vodka museum, and serving very good traditional Russian food indeed.
On a different register (and price range), the Caviar Bar Restaurant at the Europe served us a gastronomic Russian dinner which included "bear parmentier"... We returned to the Europe for their Tchaikovsky Classical Dinner evening (ate à la carte whilst listening to classical music and enjoying some ballet).
Sunday brunch at the Corinthia is expensive, but covers basically breakfast, lunch and dinner! and all drinks are included...