OK let me see if I can help. I just went and read the most recent negative reviews for the Omni.
The first one is from someone who insists on comparing the Omni Cancun to the Omni in Houston, Texas and says the check-in is too slow and there's no wireless Internet in the rooms(heathens!) Also, this person got pigeonholed by a time-share person and didn't react well to that. The person does seem to have one legitimate gripe about the A/C not working her first night, but apparently was able to move to antoher room after that. I had the same problem recently in a hotel right here in the US - A/C units can break down anywhere.
The next one is from soneone whose chief complaint seems to be that under the AI plan, she and her husband were FORCED to PRINT and SIGN their names every time they ordered a drink. Good God! As I recall, I merely had to give my room number and sign - don't recall having to print my name. She goes on to complain that there weren't a lot of special kids' choices on the menu like French Fries and mac & cheese, notwithstanding the fast food places right across the street from the hotel. Also, her room was humid (you're kidding? humidity in Cancun?) She does have some positive things to say about the pools and beach, but complains there's no nightlife at the Omni - no kidding, anyone could have told you that.
The final one is from someone who claims to be a travel agent with 16,000 customers. So right away you know they were probably a colossal pain in the arse. Anyway, this person's main complaint is that despite being a travel expert, he or she apparently didn't bother to confirm the room request for non-smoking, king size beds. So of course the hotel had trouble honoring that at the last minute. A more legitimate gripe is the mention of plumbing problems in their rooms and the front desk not answering the phone. I do seem to recall the front desk takes a while to pick up the phone at night. I suspect that some of the complaints about service may stem from the fact that the desk staff at night may not have as strong a command of English as during the day.
Now mind you, there are plenty of glowing 5-star reviews also posted of the Omni. My rule of thumb is - Expect that every hotel is going to have at least one or two bad reviews. Read them and decide if the things that are being complained about would be as big a problem for you as for the reviewer. If not, then unless the hotel seems to have more bad reviews than most comparable places, don't worry too much. When I stayed at the Omni, I recall having two minor issues - one with my room and one with the front desk. Neither was enough to offset the great service and excellent facilities I enjoyed.