If you're looking for a hotel to get a day pass at, I wouldn't get it at the Riu, I'd go to Breezes 1st. I've stayed at both the Riu & Breezes on land vacations and the difference between them is very obvious. The reason I say Breezes over Riu is that Breezes has a lot more activities going on during the day. Music, entertainment, sports, sailing, TRAPEZE(!).
I stayed at the Riu last April & I think that was only a few months after they opened. Maybe things are different there now, but unless someone can say they're different, the Riu was sorely lacking in things to do during the day (and actually at night too, we were always over at Atlantis instead). While the Riu is right next door to Atlantis, you have no access to any of the Atlantis amenities. You can walk on the beachfront, but that's it. I guess if you are looking for a super relaxed do nothing day the Riu would be satisfactory (do they even offer day passes, have you checked?) You can get beach chairs and drinks for free.
Breezes has a "spring break" policy in effect from Feb.-April-ish where you have to have at least 1 person that is older than 21 in the room with you. Also it is always I believe 14+ resort so you generally don't have a lot of rambunctious kids around. We went during "spring break" as that is the time my friends and I usually vacation. We were very pleased with Breezes. HOWEVER, with the Riu last year, there was a very large group of high school students from St. Louis who were extremely obnoxious and loud, as were the parent "chaperones". (Really the parent chaperones at times were worse than the kids! No wonder the kids behaved as they did!) If you check out tripadvisor.com for April of last year, you will find many complaints (including from one of my friends) on this group. Riu does not have any sort of policy on who's allowed to book and stay in their rooms.