I've been to Vegas many times and each time, I stay at a different hotel, but the Bellagio is very memorable. The lobby can get pretty noisy but there's so many options for activities and it's just a beautiful hotel. The water show is also fun to stand and stare.
The restaurants Jasmine and Olive were actually rather good and great views of the water show as well. We were seated right by this gigantic window. I'm also a fan of the hand blown glass in the lobby.