I went last night. It's was ok, nothing spectacular though. It was pretty reasonable priced though, which I was suprised at for Fenway. Tacos (2) were around $6-8, as were apps. Entrees were $15-20, but I did not try them. Cheek and tongue taco wasn't bad, but I had it at Taquira el Amigo a few days ago and they don't even compare. (One point of clarification, the cheek and tongue were mixed together at Barrio and were seperate tacos at El Amigo.) Fish tacos were odd in the fact that they were cubes of fried fish as opposed to one whole piece. Also had a sweet potato and shrimp tamale that I would not reccomend and a quesidilla that was good but small.
Looks to be pretty similar to La Verdad, but I prefer La Verdad over Barrio Cantina.