The family i married into is mostly Lebanese. So needless to say they know their Lebanese food. Their go to place in the city is Garage Beirut. Last summer I went to Beirut for the first time and had the traditional style meal and its very very close to Garage Beirut.
What I would say is you really need to know what to order in Garage Beirut. Here is what my fiance's family orders every time we go: Fattouche Salad, Hummus Lahme (this is to die for), Rikakat bil Jebneh (cheese rolls), and the Mixed Grill, if you are new to this type of cuisine and open minded end with the Kenafe!