This is one of our go-to Mexican restaurants. Casa del Sol is fairly cheap and the food is good. I haven't had anything there that I was disappointed in, and I've gone many times since I moved to Madison in 2007.
The margaritas are great - get them on the rocks. I've always enjoyed blended margaritas, but I converted here. I really love the salsa, though my husband would like it to be a bit spicier. I've never had bad service. Overall, it's a great place with decent prices.
Unfortunately, it seems that it is now closed. The last time we went, there was a sign saying they were closed for renovations until early 2016. It is now showing up on Google and Yelp as closed permanently. Bummer if that's the case!