There are a few Oasis resorts in Cancun. Which are you staying at?
I stayed at the Oasis Cancun. Will not do so in the future.
Why? The Oasis Cancun is situated close to a sewage treatment plant. On most nights, you wouldn't even notice it. Unfortunately, I think the plant was doing maintenance one night, because whole area near the hotel smelled like a fricking sewer. Not just outside the building, but ***inside the hotel rooms as well***. Basically, the sewage smell got into their HVAC, and permeated into the rooms.
Couldn't sleep through the stench, so I called the front desk to get another room. Their feedback: It wouldn't matter, all the rooms are afflicted by the odor.
For the most part, the Oasis Cancun is a fine place to stay: good food, quiet beach (but within close proximity to the busier parts), reasonable rooms. However...