I live in Manhattan. As a 20-something resident I have a lot of thoughts on living in New York, but in short, don't move here. The pro's and con's, most of which have been covered, are apparent. Weather, cost, people, career opportunities are all as advertised. NYC has amazing opportunities, but virtually all of them are replaceable.
Nearby: Others have mentioned beaches, mountains, nearby cities. Non-existent. It is extremely expensive to get out of the city and takes a lot of effort. A trip to the Catskills is difficult, let alone ADK. New York revolves around money. The “beach” is the Hamptons and it’s a $4,000 summer time share. The airport is a $50 dollar cab ride or an hour train. Factor in that a 9-5 workday in NY is more like 8-7, + a late night or two, + a few happy hours, + exercising to stay sane, by Friday you have no time/motivation to leave the city.
Nightlife: I'll try to be objective, if you like clubs or exclusive events, nyc is great. But for the vast majority of people, nyc has more expensive options that all cities have. You will never convince me that any growing, young city that has more than a few hundred thousand people doesn't have the same dining/nightlife/concert opportunities as new york.
People: There are pretty, smart, interesting people everywhere. If a selling point for moving to New York is banging models, NYC is the place for you.
Cost: You’ll spend 1,200-1,800/month on housing guaranteed. And overspend on every other item you buy. You can be frugal, but there is a lot of pressure to do “cool”, expensive things. Housing, transportation, etc are unavoidable.
Running: Bad. Along the water and Central Park/Prospect Park off-peak are nice. But that’s basically it in the 5 boroughs.
tl;dr: All my friends live in New York, I am paid well, and I have a great time here because of my social network and finances. If I could work somewhere else, near friends, I’d do it in a heartbeat. NYC is an incredible place, but nothing compensates for how expensive and unhealthy the lifestyle here is, and that is only perpetuated by the 20-somethings who move here for a job they don’t like, overpay for an apartment they don’t like, to eat nice food, drink $8 beers, and be around similar people….and bang models