Four of my friends and I went for Afternoon Tea. The servers were attentive and the food was good. The reason for 3 stars? Compared to Afternoon Tea at the Four Seasons, the "whole experience" was just not there. The Four Seasons tea was in the Veranda dining room. The ambiance matched the china setting on the white linen tables. At the Bellagio they had the china and linen all set up and the decor of Petrossian was fine only along one side. As long as you keep your vision on the back wall and not look into the casino, that is only blocked by archways.
This is what it lacked. The Petrossian is a bar/ cocktail lounge open into the casino. Even though they seat you along the back wall you can't help but to hear the dinging of slot machines, smoking from the bar and casino, the usual noise in a busy casino and a unattractive view of slots and people walking by. The Veranda is an overall polished experience. The Bellagio? A way to make extra $$ during the slow hours of 2-5 in a piano bar.
I guess it depends on what you are looking for. For nearly the same price, I'd go back to Veranda.