My husband and I went to Brioso last night and really enjoyed it. It's definitely not authentic mexican so if that's what you're looking for, don't go there.
I had the watermelon-key lime margarita and they were delicious with a strong fresh watermelon flavor. My husband had a traditional margarita but it was their specialty version with an upgraded tequila. It was also delicious and had a nice smoky flavor (similar to Tre Generaciones tequila but it was a different tequila). We split the tuna tartare appetizer. The tuna was mixed with cilantro, ginger and jalapenos and was very light and was served with tortilla chips. It was excellent. I thought the complimentary tortilla chips and salsa were very good although the chips are the heavier style that are served all over Chicago. I prefer a lighter chip.
We both ordered the tacos--a choice of three served with a green salsa (containing chunks of fresh avocado) and potato hash. The shrimp were excellent as previously posted here. I also ordered a chicken/portabello/cheese taco that was very good. My husband also tried a pork taco and a zucchini/red pepper/local corn taco. The latter was his favorite (along with the shrimp). For dessert we split a coconut ginger flan and had coffees. We're not big fans of flan and were very surprised by how much we enjoyed this. It was a coconut flan in a pool of clear ginger sauce. I thought the portion sizes were good and we were very full when we left.
Our server failed to tell us of the specials and our food came out a bit too quickly, but those are my only complaints. We really liked the modern but comfortable atmosphere and absolutely loved the music (Stones, Fiona Apple, LCD Soundsystem). We weren't expecting authentic mexican given the description as "Modern. Mexican." and the postings here and really enjoyed our experience overall. We will definitely be back.