I really liked this place and I was disappointed there was only one other couple eating when we went. 90% of Mexican food in Vegas is inexplicably bad, but this place hit all of what makes a place good for me:
Queso (could use some hot peppers but still good)
Choice of whole beans rather than refried
Non boring non meat options
Free chips
I had the Burrito El Gordo, which is a burrito full of a crispy chile relleno. The waiter recommended I change the sauce to the chipotle sauce which was actually spicy and really good. I am looking forward to going back and trying other things. The only thing I wasn't a big fan of was the salsa, but otherwise one of my favorite Mexican in Vegas.
Also, the comparisons to Roberto's are super weird because Roberto's is so bad and not even similar.