Notion is an excellent restaurant. The chef combines restraint and molecular gastronomy to produce some very interesting food that excites the eyes, mind, and palate. A four course meal runs $65 plus tip (BYOB), and you can opt for a longer tasting menu. The 4-course meal includes a number of amuse bouches, and is quite filling. Nothing is a la carte. I heard there is a vegetarian menu, but you need to call in advance.
I would not say that the meal I had at Notion was one of the best meals of my life. It was perhaps the best meal I've eaten in Pittsburgh. As the meat is cooked sous vide, I would recommend ordering beef and other meats that are perfect when cooked at a uniform texture rather than something like duck, which is more exciting when there is variation.
The interior is minimal and tasteful. The noise level is low. Most people seemed quite dressed up for Pittsburgh. Definitely a great place for a date, dinner with friends, or a business dinner.