This is just a race that you HAVE to do if you get the chance. The course is awesome (minus maybe the 3 seconds you're actually in the Bronx), the crowd support is off the charts (especially Brooklyn & Central Park), and the field has a really cool international feel to it. The elevation is sneaky difficult with all the bridges, so prepare for hills.
Logistically, this race is insanely tough to pull off, so I'm impressed it was done so well. Be prepared to get up super early to leave your hotel and head to a bus or ferry to get over to Staten Island. Once you get to your chosen mode of transport (which you pick during the sign-up process), they take it from there. Once you get there, you'll probably be there for quite a while before the race actually starts, and if it's cold (like 2013), you'll want to be prepared.
My main gripe is that at the starting line, they instructed us to ditch our donate-able sweatshirts & pants too early and we were stuck in the cold for 30 minutes waiting for the gun. So plan on wearing lots of throw-away clothes, and keep them on as long as you can (but don't throw them on the bridge...they don't like that)!
Also, with so many people, be prepared to be log-jammed at the finish line for quite some time. It took me an hour to get out of the finishing area to meet my friends. But when you have 50,000 people and who knows how many spectators descending on Central Park, there's no way around it...you just have to factor it in.
Overall, it's an amazing experience that is worth the wait if it takes you a few tries to get in through the lottery (4 years for me). Chances are, with the $250+ price tag and high hotel/travel costs, you may only do it once.