Now, this is going to be completely completely subjective and based off of my own personal preference for foods, but I've consulted with most people in my program and here's a brief list of three great-must-try restaurants of Santiago when you study abroad.
Let's start easy and cheap but still delicious! Pan y Oliva! A friend of mine that lives in Providencia actually recommended this place to me as a late night eat after we went to the gym one day and were totally starved afterward. Let me tell you, this place has insane sandwiches! If Santiago does anything really well- it's probably avocado and sandwiches. That night I order a quinoa burger on pita pan with avocado and this thing was so big I had to ask for a knife and fork to eat it because 1.) my food was falling out all over the place 2.) I felt like I looked ridiculous because of said food falling out all over the place and all over my face.
There are no seats here and the decor is just white modern white tile. The owner of the place is incredibly incredibly lovely and even opened up one day when he wasn't supposed to be open for my friend, because he had called and told him that he was so hungry. I recommend Pan y Oliva as a great option for a killer sandwich with great sauce for a reasonable price. My sandwich cost 2.900 (around $4.50) plus you can add extra things for more. Give it a try. It's also pretty close to Campus Oriente- which is where all of GW's courses are, so it's a great option after a late night class. The most important thing to know is that it opens at 6 pm (I know- kinda late).
On to option number 2! This restaurant is a better option to sit down and eat in the Providencia area. I welcome you to...El Huerto. One of the best known vegetarian restaurants around. I think it's even ranked globally! These guys have a super cute feel and is a great option on a nice warm night because they're outdoor seating is perfect. They give out pretty big portions, and in my opinion, you can just order two starters and be happy. Regardless, they have great flavors and a variety of options for plant-based diets that even your omnivore friends would like. You just don't have to tell them ahead of time that El Huerto is a vegetarian restaurant... Just hold on to that detail until the last minute. They might be upset at first, but as soon as they're fed they won't mind. Great option! Relatively well priced! Obviously a bit more expensive thatn Pan y Oliva but nothing ridiculous whatsoever.
On to the ultimate and my favorite favorite restaurant in Santiago. This option is for when your parents or aunts or relatives come to visit and you can afford to go out a big more expensive. Or, maybe an end-of-semester dinner or my program has plans to go in a couple of weeks when one of the girls on our program graduates from GW but won't be able to attend graduation. Anyway, the final choice is: Bocanariz. Probably the biggest con about Bocanariz is that it's so popular- it makes for a great gringa spot. When I went, most of the patrons were speaking English- so this isn't your best option is your looking for something more local, like Pan y Oliva. Bocanariz's menu isn't divided up normally with appetizers, entrees and deserts...but rather, it's divided by harmonizing flavors. You if you're feeling something smoky, they have a list of smoky apps, entrees and deserts. The list continues: smoky, sweet, salty, aged... you can really pick a great meal based off of how you're feeling that day. The service is great- as in most places in Santiago- and you can really take your time to enjoy having a special meal. I'd personally recommend the risotto with herbs and mushrooms (and that cheese plate looked pretty good too!).
Best of luck in your culinary adventures in Santiago and I hope you find your own (and maybe better) spots. Obviously, the most interesting things you'll probably eat is what you eat at home with your host family- or all the exotic fruits and veggies they'll have you try (I have no idea what I am going to do when I am back in the States and I don't have accses to cactus fruit). Enjoy!