Let's get a few things said right off the bat. El Rio Grande is not a groundbreaking restaurant. You will not find things that you've never seen before at typical Mexican restaurants. What you will find -- however -- is a well executed "been done before" idea. The chips and salsa is to die for. I'm not sure if they put rum in the salsa but in my opinion, it is the best salsa and chips I have had in the area.
The Vegetarian options are friendly and accessible. I hate having to order a pork taco with no pork. I love being able to point at a Vegetarian combination option and its a done deal. The wait staff is generally prompt. Only a couple times out of the many times I have been there did I find the wait too long either on food or service. They have grown some menu items lately as well such as the spinach and mushroom quesadilla which is delicious.
Lastly, the prices are satisfactory. Besides the affordable lunch menu, dinner is also a treat. Soda is typical fare but they do also offer Jarritos last time I checked. They do have some drinks like margaritas but they are working on adding, what it looks like, is a full bar. If that pops up, it will definitely be interesting. Beware! Parking can be very difficult especially during peak times and you may be forced to park on the street if you are desperate. Despite that, there is usually more room inside then parking space.
But anyways, a place like this in a small town like Stoughton is a great option. It tastes wonderful, the prices are reasonable and you'll leave and want to come back -- the perfect recipe for a great meal.