Decent, but not great compared to Harrahs\Caesars Palace\Paris\Planet Hollywood Diamond Lounges. Went during a weekend and it was PACKED. There were literally no seats available. Waited 10 mins and someone up and left, so swooped in and took the seats. The table barely could stand on it's own and wobbled precariously every time a drink was set down. Moved to another table eventually and same scenario. Temp was a bit warm inside, and service was slow. They were nice, and I don't fault them for being a bit slow, as the place was completely overcrowded. They don't seem to enforce the +1 guest policy when it's busy as they should.
Of all the TR Diamond lounges in Vegas, this is my least favorite. In fact, I now avoid playing at Rio simply because of this lounge.