Huge fan of sandwich shops and Firehouse is one of my favorite chains. The meat, bread, and veggies are all high quality and toasted nicely. My favorite is the hook and ladder but I have tried many and never had a bad sub here.
Firehouse has a couple cool features that set it apart from some restaurants. First of all, they have a massive hot sauce collection that is rated 1-10 based on spiciness. Try the Firehouse hot sauce (I believe its called Datil Pepper Sauce). It is a slightly spicy bbq flavor and really adds a kick to sandwiches. Most locations also now have Coke Freestyle machines which I think are just plain cool.
I wish there was a Firehouse closer to me so I could eat here more but for now I will have to stick to tracking them down on road trips.