I suppose the Mirage would be a 5 star hotel just about anywhere else in the world. But Las Vegas is not just anywhere else in the world. It's an older property and the rooms are not exactly luxurious, but they are extremely clean and have everything you could ever need or want.
I stayed here recently after receiving an email offering a two nights' stay and two tickets to the Cirque du Soleil show, "Love." The offer was for about $150 out the door for everything. That's not a per night charge. The show tickets are not great (nosebleed) but there really is not a bad seat in the house. So two nights and two show tickets for $150 is a pretty rocking deal (and it is a great show, by the way).
Would I stay here again? For the right price, sure. It's in a good location and has all the amenities of all the other hotels. It's not a 5 star spot (by LV standards) but then again, you aren't paying $400 a night. I can live with that.