Northerly Island is a nice looking empty piece of land, but it's still an empty piece of land. I wouldn't really recommend going unless you've been unemployed for a couple of months and are desperately looking for ways to pass your time.
I think they're trying to turn it into a native habitat for birds and stuff. If that's the case, then it will eventually be pretty cool, but it's not there yet. Right now, all you get is a bunch of grass, a couple of statues and quite a few geese.