I completed the NYC Half in 2013 and it was a great experience! I thought it was going to be the same as the NYC marathon, but it's completely different! The expo is great- it can be a little crowded, but there was a good amount of booths. I received a tee and bib there. The marathon course is fantastic- it takes you through NYC and even right through Times Square. There are a lot of photographers so you wind up with really great shots. Even for being on NYC streets, the course is not congested at all. There are aid stations at just about every mile and the volunteers are great at handing you water.
The course ends all the way downtown so definitely have someone pick you up and park a few blocks away from the finish. It's NYC though, so I really didn't expect it not to be crowded downtown. You get a really great medal at the end and refreshments. You also get wrapped up in the foil to keep warm, so they really thought of everything.
I think it's a race that lives up to its hype.