HUGE and yummy sandwiches at totally reasonable prices for Vegas=4 stars. Crappy/slow service and the seeming inability to organize the seating-ordering-bringing food-paying process=2 stars.
Still, given that the food is above average and that this is maybe your best late-night option in the Mirage, I'd recommend ordering at the (very efficient) take-out window and shamelessly going to work on your pound + meat stack in the casino. There's no judgement in Vegas, right?