This was my first trip to Foxwoods, and from what I could see, the MGM Grand was by far the better hotel to stay at on that property. It's a sleek modern hotel, with a nice sized gaming floor at it's feet. You should be aware that if you're going to stay at Foxwoods, that the MGM is a good distance walk to the main casino floor of the older portion of Foxwoods - plan a good 5-10 minutes depending on the speed you walk. That being said, I largely found that there wasn't a whole lot of reasons to go to the other side of the property, unless you were specifically trying to go to an establishment over there or a show. The MGM side is much higher-end then the portion of the property, and that was visible in the trim, the machines, the decoration, and even the people - who progressively got more sketchy the further you walked from the MGM.
Room sizes were described by my friends as small, though I thought my double-queen room was just fine. The bathroom had a shower only, no bathtub - which is fine in my book - and the shower had very hot water with tons of pressure. I do think it's worth noting that the primary credenza in the bedroom was a little beat up - chipped and scratched along the leading surface, though the room showed little wear and tear anywhere else. The only other thing worth noting is that the TV in the room is grossly undersized in this day in age for a hotel TV, the remote barely worked, and the on-screen system was slow to respond and just struck me as odd.
The friend that I stayed with was woken up in the middle of the night by loud music that came from what I only think was a batchelor party going on down the hall - he didn't call to complain, and I slept right through it.
All-in-all, I would stay at the MGM again - I found it far nicer than the rooms at Mohegan Sun, though I like the offerings and layout at Mohegan better.