We stayed at the Monte Carlo in the summer of 2013, primarily for the pools. The pools are pretty awesome. There is a regular pool and hot tub, a wave pool and a lazy river. It was very fun and relaxing to float along the lazy river. The tubes weren't too expensive for an all day rental. I think about $10.
The whole pool area has a fun vibe. There is good music playing and the staff is friendly. The drink prices are a little higher than other Vegas pools I've been too, but it's doable.
There are plenty of chairs around and the area is very clean.