Bellagio hotel is one of the nicest hotels in Vegas. I have stayed here a few times, and my most recent stay was last week. The staff continue to be very attentive and wonderful. Reserving a lakeview room or a one or two bedroom suite that overlooks the lake is a plus! The pools are dreamy and gorgeous, and you do need to get out there pretty early on the weekends to get a lounge chair.
The hotel also has a wonderful art gallery (Bellagio Gallery of Fine Art), a great selection of restaurants (Circo, Fix, Yellowtail, etc) and wonderful shopping. Their show "O" is pretty amazing also- that is a must see!
It's just a very classy, upscale place and one of the best places to stay at!