2 slices of pizza and a soda cost $12! More expensive than New York.
As you see it sitting out on the counter, you had a feeling it wasn't that great. As you order, they warm it up in the oven and serve it to you.
When a pizza got low on the display, they simply stuck a pre-made pizza in the oven. There was a whole rack (probably 8-10 pizzas) already pre-made waiting to be placed in the oven. No telling how long it has been sitting on the kitchen counter but I'm guessing it doesn't help the freshness.
If you have a choice, go elsewhere. Heck, take the tram to Mirage as the TI buffet is also bad.