Maybe Sanhattan is not even similar to Manhattan, but this is the way in which some like to refer to it. Even though, one of those guys made a Wikipedia entry about it. The first line of the article states that the place is "Chile's capital Santiago's high-end financial district". This is only half true because the Santiago Stock Exchange is at downtown and there is where most of the transactions and exchanges are made. But what is true, it's the fact that most of the biggest companies and most important consultant firms and service providers have their headquarters.
The location is very nice. There you can find a mix of corporate buildings, offices, residential apartments, groceries, drug stores, restaurants, banks and plazas. In the recent years its influence has been growing, but I personally believe that Downtown Santiago is still the most important part of the city (historically, culturally and economically).
Touristically speaking, the neighborhood is a very nice place to visit, considering the fancy restaurant, popular bars, five-star hotels and eccentrics buildings. However, you need to be aware that this is the workplace of thousands of workers, thus the traffic is awful, there are few places to park and the public transportation is almost always overcrowded.
I don't know Manhattan, but searching on the web it seems that Sanhattan has similarities with its New Yorker counterpart. It's like Europe or USA; if you're a westerner, you'll feel as you were at home.
