I've stayed at The Rio on two Vegas trips, one time back in 2005 and on my most recent trip a few months ago.
The first time we got to stay at a Masquerade Suite. The suite was very roomy and had floor to ceiling windows with a wonderful view of the Strip. Access to the Strip was pretty easy since it had a shuttle that took you to Harrah's and back. And food-wise, both the Carnival World Buffet and Village Seafood Buffet were good enough to satisfy our hungry stomachs. I also enjoyed the festive atmosphere in the Masquerade casino area. It was a great experience.
Fast forward to 2017 the experience was just slightly underwhelming, but still okay for the most part. This time we stayed in a Classic Suite so the room was much smaller. Didn't matter too much to me though since I pretty much was only there to rest and sleep. Amazingly, parking is still free in their self-parking garage. Since I had a rental car, that was a huuuuuge convenience for me. The Village Seafood Buffet was no longer a separate buffet and had been absorbed into the Carnival World Buffet. The downside was that it was only open for dinner only. Because I had made dinner plans for other places around Vegas, I didn't have time to check out the buffet.
Overall, The Rio has been a good resort to stay at. I haven't really taken advantage of its amenities because I only stayed there to rest and sleep, but I did like how it's conveniently located within close proximity to the Strip and Chinatown which made it easy to travel by car.