I've been to Matt's a bunch of times when it was the small house on the corner and now at it's larger location. On the weekends there always seems to be a huge line. At least now they have more seating.
The food has always been great, but the line is always way too long. When we were there last, people were piling into the cashier area waiting inside because of the warm weather. They packed into the restaurant and crowded around us at the front counter. I definitely didn't like the feeling of people hovering over us while we ate. Some were even rude enough to be leaning on the counter that we were eating on. Overall not an enjoyable experience.
I like the overall vibe of the restaurant and the food, but because of the lines, I'd opt for another breakfast spot. The Valley has plenty of other amazing breakfast/brunch spots.