Cosmo is a very beautiful hotel. I believe this is the only Hotel that has balconies so you can enjoy the Bellagio Fountains without leaving your room ;). They have literally everything inside: restaurants, mini shops, bars, nightclub/dayclub Marquee (which I love and will do a separate review on that). They even have a little FedEx center.
We stayed at this Hotel 4 times during our trips to Vegas and we loved it. We normally get Terrace 1 Bedroom Fountain View and it is amazing. I would not suggest any other one for two. The rooms are gorgeous and their staff is amazing. Shoutout to the Roomservice department, we love you :)
The Chandelier bar is a top notch. Very beautiful and I love their cocktails. Also the Eggslut sandwich place and The Juicestandard are pretty yum.