I have attended a few events at the MGM Grand Arena. As far as large venues go, this Arena is not my favorite, but it gets the job done. Besides, it's not like you get to pick where you are going to see your favorite singer perform, or catch the next UFC fight...
I like that there are ample places to buy the extremely high priced alcoholic beverages. I dislike those prices but it's the Strip, know before you go and preparty!
It's true that there isn't really a bad seat in the house. I have never spent top dollar for my seats and have always been a-ok with the view and acoustics. What I DO dislike about the seating, at least in the section I sat in last, is that the seating moves when anyone in the row gets up or sits down.
Least favorite part of the Arena? The parking garage is a clusterfuck when leaving. Next time I have an event to attend at the Grand Garden Arena, I am going to take the advice of a fellow Yelper and park at another casino and take the monorail to MGM.