Good food, great service, outstanding views!
I've come here every time I've been to Vegas and have tried every possible meal from breakfast to a late dinner. The best time to enjoy Gabi's is at nighttime: the Bellagio fountains will be going off every 20 or so minutes, the Strip will be packed, and the patio cool and pleasant even in the summer months. However it can get crowded in the evening so if you want to sit outside be prepared to wait for 20 or so minutes and get a reservation in advance. I've come here with a friend once without reservations and was told there would be more than an hour wait to get a seat anywhere on a Saturday night. Since the restaurant is so versatile it's hard to recommend 1 or 2 dishes in particular so it's probably best to list the highlights by meal:
Breakfast: Croque Madame or the Quiche Lorraine. Help yourself to some champagne too, it's Vegas
Lunch: Chilled zapacho, Seafood Crepe, and the Trout Amandine are all great. On Friday they serve an Australian cod which is brilliant
Brunch: Do yourself a favor and order a French 75. It's no longer on the menu but they make the best in town. Add in the Eggs Benedict and it'll rival Bouchon for the best French-themed brunch in Vegas.
Dinner: The Seafood Platter is the best deal for an appetizer. 50 dollars for a whole lobster, oysters, tuna tartare, shrimp and even more. Follow that up with the Steak Bearnaise or Roquefort and finish up with profiteroles accompanied by cognac. Be careful: the calories will add up but it will have been well worth it.