Sleepy Hollow/Hudson River Valley
 

We are considering visiting this area this summer. Has anyone been there lately? Also, what is the best way to see Long Island? What is open there, what do you suggest? We will be there on July 4th.

On July 4th weekend the best way to see Long Island is by helicopter.

Everything is open and everything is mobbed - with the addition of a variety of local parades and fireworks displays at night.

The public beaches nearest the city will be mobbed from 10 am. The north and south fork will be mobbed with house sharers as well as many families and singles on either a week's vacation or a long weekend.

Evey road will be packed from early hours. Unless you're going to a specific town and want to stay there (staying with someone with a car) driving is the only option - since on the holiday weekend public transit (except LIRR to and fro the city) is essentially non-existent.

Don;t know opening hours of Sleepy Hollow - you would need to check the web site. It would be less crowded than the beaches (any place is less crowded than the beaches) and is well worth a trip.

Sleepy Hollow is a village in Westchester County. What exactly do you want to see? Kykuit, the Rockefeller estate is there (well, actually in an adjacent village, Pocantico Hills), and there are many other sites in the area.
(PS: I don't know what nytraveler means when saying, "the opening hours of Sleepy Hollow"! The opening hours of what?)

Well, if you wanted to pick an "appropriate" Sleepy Hollow site, it would be Sunnyside, the former home of Washington Irving (which is actually in the next town, Tarrytown). BTW, Sleepy Hollow has only been an official town name for about 10 years years. It used to be North Tarrytown but it was changed to make the most of the publicity

For the sake of accuracy, Sunnyside is in Irvington (just south of Tarrytown).
I'm still not sure what the OP meant in mentioning Sleepy Hollow. While it's a charming little cottage and worth a brief visit, Sunnyside is hardly the prime site to visit in that area!
Just to mention a couple, Kykuit and Lyndhurst (the Jay Gould estate that was used in the filming of "Dark Shadows" a few years ago) are much more interesting!

How long is your trip? What do you want to see on Long Island? Where on LI will you be staying. It's, as it's name suggests, long so it's a big place.

The ONLY way to get around on Long Island is in a car. The public transport is awful to non-existent so you must rent a car. Since you're planning to be in NYC, I wonder why you'd leave on the 4th. The fireworks in NYC are fantastic and it would be a shame to miss them. Most of LI is suburbia. Unless you have friends or family there or HAVE to go to the beach, I'd give it a miss.