Good place but know what you want from a location before booking
We hadn't booked accommodation about a week before we were due to arrive in NYC, so many of the TripAdvisor top recommendations were booked up. Added to that, prices were very high for anything that didn't look like too much of a gamble.
We stayed (3 adults and 1 child) in mid August 2012 and found it to be a good place - but there are some qualifications to that statement: 
1. As we stayed over a weekend, we noticed that this Marriott had a comparatively good rate - if I had payed midweek rates I think I'd have been (much) less impressed.
2. While the location is right by the Trade Centre Memorial and is convenient for Battery Park Ferries, there is little else to see beyond Walls Street. However, the subway network is very good indeed from the location and therefore getting around is very easy, especially if you buy the Metro passes. 
3.Because the hotel is situated on West Street, its is also easy to get a taxi uptown or to the East side quickly and quite cheaply.
As for the hotel itself, it was clean and well appointed. Everything the Marriott usually is and promises. Check in was efficient and staff in general were polite and friendly. The rooms were clean and spacious and the bathroom well appointed.
We ate one evening in the restaurant and it was disappointing for the price - we found other places around and about to be much better quality.
Because the hotel seems to principally cater for weekday visitors, we found it to be a bit soulless and lacked any real charm. The only common area was a rather scruffy lounge with poorly laid out seating. 
All of that said, for the rate we paid - about £200 per night - it represented much better value than much else on offer at the time. So provided you don't mind taking the subway and aren't expecting an interesting hotel with a lively nighttime scene, then it definitely does what it says on the tin.