My observations of NYC EMS are anecdotal at best, so just be aware of that before I start. I work in Ohio and not NYC, but I have friends who work there and I have also looked into it myself.
1. Pay is crap, I mean super crap. Especially as an EMT-Basic, you most likely will not be making enough to live on in NYC. If you end up working for FDNY/EMS, you will be mandated to live in one of the 5 boroughs.
2. Job market is public safety is tight everywhere. Your options for EMS there are FDNY/EMS or any of the hospitals that run their own EMS. I'm honestly not sure how this system works, who gets dispatched when a 911 call is made, so maybe someone else can speak up on that. I will tell you from countless stories that I've been told, FDNY/EMS guys are treated like garbage from the FDNY/Fire guys.
3. It's my perception that the run volume in NYC is quite high. I'm currently working full-time at a fire department that also has a high run volume (avg 18 runs per 24 hour shift, we all know by the law of averages that this means some days we run 10 and others we run 30). I mention my background because running in a high volume system is fun for about 2-3 years, after that it's just burnout.
4. I'm not sure if they run 24 hour shifts (24 hours on, 48 hours off), or 10/14 schedule (2-10 hour days, then 2-14 hour nights, then off 4 days) or simply 8-12 hour shifts for 36-40 hours per week. No matter what the schedule is, count on the following
a) Don't plan on studying at work. If you get the chance, then it's bonus, but don't ever leave things to the last minute and plan on getting them done between runs, it WON'T happen.
b) Scheduling in-class school always becomes a nightmare, especially with the first two shifts listed above.
c) The advantage is, down the road when your resident cohorts are exhausted post call, you'll have had years of experience of being up all night and not really understand what the problem is.
EMS is a good place to get your feet wet. You will see a lot of bull-crap patients, but you'll also see a lot of really sick people. You will be doing things that impact a person's long term outcome. It is backbreaking and mentally exhausting work, but every now and again it can be quite rewarding.