I've stayed at the MGM Grand 3 years running in January for the Consumer Electronics Show. I've been pleased with each visit
The biggest complaint I've ever run into is that the length of the hallways is ridiculous. That may not sound like a big deal, but it can be given the size of the overall property. The property size is a plus in my book because it makes the place all inclusive in a lot of ways. If you're up early or late at night, there's always something open for you to eat or drink.
The rooms have always been in great shape during my visits. Room service has always been timely and I've never experienced any issues with the staff. One thing I like about the room is the black out curtains. They come in very handy if you're working or partying on a weird schedule.
We'll be staying there again in early January and I assume the experience will be the same I've had in the past 3 years.