I've been there twice: once for a meeting and another time for lunch with my husband.
Their food is fantastic and their service is fast and friendly. Both times I've eaten there, everyone working there had a smile on their face and was very accommodating.
I absolutely LOVE that their rice and beans don't have any animal broth or lard. Even their tortilla chips are lard free! This is difficult to find in a mexican restaurant.
I love that they have vegan options too, like the bean chimichanga (as well as a few other vegan menu items that I can't quite recall at the moment).
The fact that Don Ruben's has some vegan options for me and then some meat-themed options for my husband means that we can enjoy a wonderful meal together!
I can't speak for myself, but my husband says that the meat dishes he's eaten there are also wonderful.
I recommend that you give Don Ruben's a try!