Having visited Boustan one too many times during my final's week, I can safely say I'd go again. The service is fast, you can thankfully sit and eat if you don't want to leave. From the outside, it looks like a small hole-in-the-wall a la Chez Danny style but there are a few tables constantly vacant since most of their clientele are students that have to get back to Concordia for their following class.
The selection is quite typical of Lebanese restaurants. Shish-taouk, Shawarma, garlic potatoes, etc. (You know the drill if you are from Montreal). Nonetheless, the food is still quite good and well worth the price.
One thing that I'd warn against: their shish-taouk sandwiches are pretty greasy. My Lebanese friend, who probably knows every single Lebanese restaurant in Montreal, also noticed the same and called Boustan "inferior" and told me "they lost the way of the holy pita sandwiches". Don't hold it up too long or the grease will fall through the paper. I had to clean up a mess on the 8th floor of Hall because of that.
It's quite typical and nothing to really gouge your eyes about. I'd recommend chateau kebab over Boustan to be honest.