This was on my must try list on my most recent trip to Vegas. We came here for a late night snack at midnight and the line was still insanely long. I ordered the shack stack and a side of fries.
Shack Stack: 4/5 stars. Delicious! Especially with that fried Portobello mushroom with cheese oozing out yummm. The burger was smaller than I thought it would be... so it's definitely a bit pricey considering it was almost $10. It also came out lukewarm--it would've been even better had it come out hot.
Fries: 3/5. Pretty standard fries. Came out nice and hot.
We came back the next day to try their concrete and I must say that I was immensely disappointed by it. We ordered a vanilla with the truffle cookie dough mix in and a vanilla with strawberry puree mixed in. It wasn't really anything special and for about $4 a scoop I should've just gotten regular ice cream elsewhere.
Overall, I would come back for the burger but I would skip the custard and concrete.