I am an American married to an Indian and I must say the food is very authentic. This place is frequented by mostly the natives and that usually is a good indication. The food is not only pipping hot and delicious, but its also ridiculously cheap. Try the Madras coffee (served in the typical south Indian style of a tumbler & a bowl) or an amazing Chai for just $0.79 ! Everything on their menu is less than $3-4 and portions are quite big.
The place has regular south Indian fare like dosas, idlis, upmas but also specializes in Chaat stuff as well as other Indian fast foods. I highly recommend the Special Thali (which is big enough for two people to eat) or the Madras Thali($4.99). My wife tells me that the Chaat here tastes a lot like she had it in Mumbai. I highly recommend the place.
PS : The food here tends to be on the hotter side for Americans, but you can ask them to tone it down.