My husband was niftar 10 years ago--we owned our house jointly in the USA. He left a will stating I was to get all assets. I understand halachically that my only son (there are daughters, too)should be the actual inheritor, and not me. Is this true? I believe that Rav Moshe Feinstein stated that wills in the USA are considered halachically acceptable. Or can my son write a form of "shtar" stating he gives me the assets? I gave him all the seforim and religious items years ago.

The halachot of wills and gifts which are in contradiction to the laws of inheritance are complicated, and a competent posek should be consulted about a specific case. An excellent article on the issue can be found at this URL.