I heart this place and go every time I return to UIUC. (Which is becoming harder to do as I get older...)
The food is delicious and what makes me want to come back. The vegetarian combos are particularly good, too. Mom & pop-style Mexican food - none of that Chili's/Chipotle nonsense.
Service is prompt and your food is there before you know it. My imagination leads me to believe that there is a Dos Reales Pit Crew that is timed from order to table delivery. Prices are reasonable and it's great for groups.
And the margaritas, oh the margaritas. =)