I really enjoy staying at the Bellagio whenever I'm in Vegas. The first time I stayed here I had tickets to go see O (Cirque du Soleil) which has been in permanent residence at the Bellagio since 1998. If you're staying here, make sure you go see this amazing water show for sure!
The actual hotel is gorgeous and there's plenty of activities in and around the hotel. I definitely recommend getting a fountain view suite with a king size bed. Amazing views at night and nice accommodations.
And if it's in your budget, make sure to indulge in some of the services at the Spa and Salon at Bellagio and shopping. Believe me, it does a body (and mind) good.