Louis Lunch is a big no, as far as value is concerned. At least food value. They only value is in being able to say that you’ve been there. It has a lot of that.
We tried Modern once about five years ago. It does not remotely belong in the same category as Pepe’s or Sally’s. It bears comparison with Yorkside; i.e., if what you want from pizza is being pretty much just like Papa John’s or Domino’s, but maybe a little better, it’s fine. Despite its name, Modern has been around for a long time, but I never heard it was any good until recently. We were a little surprised to find that it was only a block and a half from the house where my wife lived her junior year, and neither she nor (as far as she knew) any of her housemates ever even tried it.
I third or fourth the recommendation to visit the University Art Gallery – it’s now stunning. If you’re there in the evening, and you have a chance to go to the Yale Rep or (if you are there at just the right time) the Dramat, that’s a lot of fun, too.