I will admit MGM is not the newest hotels on the strip but it is definitely not old and dingy at all. People may have an impression that its old just because they know its been there a while. Our room was much larger compared to our room at PH, I dont know if its standard but it had a pretty large sitting area (we didn't do any upgrades or anything). The room was probably almost twice the size as PH. The bathrooms were nicer and larger too.
I think MGM has a beautiful lobby area but I agree with one of the comments that its a bit of a walk to your room. The elevator area on each floor is also very beautiful.