We booked into MGM for five nights over the 4th July long weekend and honestly cannot fault the service we received from the hotel and casino staff.
Our reservations were made through Trivago so we got a great deal on a West Wing King room. Yes, it is a small apartment. Yes, the bathroom is directly to your right (or left depending) as you walk in with no door to speak of and yes- no mini bar BUT- the furnishings are modern and look brand new. The room was impeccably clean and the bed super comfortable although our view wasn't the best.
After one night in our room we had a friend decide to come and stay with us so we went down to the check-in counter to see if we could secure him a room. The lovely desk lady offered us an upgrade for only $30 and we ended up in a Grand Queen on the 17th floor with an amazing view of New York New York.
Obviously the MGM has some issues eg. long check-in line, key cards that will stop working if placed near credit cards or phones etc but for such a massive hotel/casino/entertainment precinct I feel that is totally insignificant. The amenities are excellent, the staff courteous and genuinely helpful/sympathetic to your needs and the Casino itself boasts some of the best restaurants, bars, nightclubs and pool parties you can find in Vegas.
Anyone who says otherwise is just a whiner...