I LOVE the burgers here! Coming from all the amazing burger joints in LA, I would say Holstein's has my second favorite burgers ever. It beats Umami Burger for sure, is on par with Bachi Burger, but Father's Office still wins. Nothing could beat Father's Office.
Anyway, Holstein's is fabulous in it's own respect. The restaurant is casual and comfy; decorated with cute little cows. Prices are on the more expensive side at ~$15-20 per burger with a side of fries but it is located in Cosmopolitan so I think it's pretty fair for Vegas prices. Service is only mediocre to me since the waiters check in too slow at times so that's why I'm giving it 4 stars.
I've tried the Gold Standard and the Rising Sun burgers. Whenever I have these, oh man I am in burger heaven. Gold Standard has bacon, aioli, arugula, and aged goat cheddar cheese on top of a sirloin burger. The Rising Sun has a teriyaki glaze with Kobe beef and tempura avocado!! The avocado seriously is amazinggg. I definitely recommend these two burgers.
Not only are the burgers the bomb but the alcoholic milkshakes are too! You can also ask them to be non-alcoholic if you really want that. They have a variety of flavors that they rotate around. You really can't go wrong with any of them. I've had the Frozen Grasshopper, Banana Creme Pie, and Red Velvet before and they were all yummy.
Overall a fun restaurant with delicious burgers and milkshakes perfect for your Vegas gluttony!