My company's North American HQ is very convenient to HPN and I have mixed feelings. When everything works, it's wonderful- rental cars outside the door, small and very easy to navigate, etc. The gate areas can get very crowded at 5 PM- not enough seats, only a small food stand and some crappy vending machines, way too many announcements for that small space. I also suspect that when there are bad weather conditions and they're slowing down takeoffs at EWR, JFK, LGA and HPN, HPN gets the short end of the stick. If a 737 takes off 2 hours late from JFK they have far more ticked off people with missed connections than they do if they delay a Jungle Jet at HPN.
I would not use HPN if my real destination were Manhattan, although they do have train service to Grand Central Station from a nearby commuter station accessible by taxi. IMO, you need to allow way too much safety margin if you're trying to get between Manhattan and HPN by car because you never know what the traffic will be like.