Probably a 3.5 - definitely better than average, but not really authentic. That said, Border Grill is a good place to get a margarita or have a dinner with a view of the pool.
I wasn't drinking, so appreciated the good sized selection of non alcoholic juice drinks. Sometimes these are sugary and gross but my pomegranate limeade was delicious and I didn't miss the alcohol (too much...)
The guac was really "meh" as were the trio of salsas that came first. The green one was the only one with any real flavor. My carnitas plate was also "ok" - the meat was a little dry and definitely on the salty side but the veggie slaw was refreshing and crisp.
Definitely one of the better "reasonable" options in the Mandalay.