Many years ago I remember my first time ever paying for a buffet using a machine in the wall. After standing in line for hours at places like Bellagio or Paris I welcomed the technological advancement. This place is huge - you obviously don't get that personal touch that maybe some thirst for so much... but for the record I am a self check out kind of person and don't mind.
If you are a Platinum or higher rewards member you get that extra attention and better treatment. You get to skip ahead the line and go into a special room to pay. Its nice, trust me. Make friends with a whale if you can.
Food is very good. Enough people go here and it is popular enough so that food is fresh. Amazing dessert selection. Fancy ice creams -- be sure and leave some room.
A solid choice especially if you are staying at this resort. Really, there is no reason to ever leave the Rio during your entire stay. Pool is great, buffet is fine, Voodoo lounge has unbeatable views and is a good value.