Huge hotel, we stayed in one of the suites. OK value for money, but the hotel has no personality, is quite outdated and rough around the edges. I would not say that this is a 5 star hotel. Unfortunately we got food poisoning after eating in the hotel café on the ground floor right after we checked in. After that, we spent 48 hours inside our room, too sick to leave. We notified the staff several times about our situation, but they seemed unbothered about the fact that their food had made us really sick. In general, the hotel staff were quite unfriendly during our staff, including the interactions with room service employees to the receptionists and bell boys.
When we checked out, the only thing our receptionist said to us was "That's it". That pretty much sums up the level of friendliness at this hotel.
There are plenty of good 5 star hotels in Panama city with great customer service. For example Bristol, where we also stayed during the same trip. Would not recommend staying at Riu Plaza.