Its commemoration, annualization, and celebration as a particular national holiday has played an important role in (and in maintaining) USian mythistory, mainly in falsely presenting early US settlers as peaceful, native-friendly religious refugees with no colonial aims or genocidal intent.

Leftists and indigenous Americans are critical not just of the ideological role of that national holiday as such, but are also attuned to how disgusting, callous, and hypocritical is the thought of celebrating one's 'good fortune' to 'find themselves' settling such a catastrophically, genocidally depopulated environment. The latter criticism arguably applies to all 'days of thanksgiving' celebrated in this tradition in what would become the United States and Canada, and not just the big national holiday.

In the contemporary context, Thanksgiving is one of a few national holidays for which most USians customarily get (or try their damnedest to take) a day off. (At my employer, it's the most 'generous' holiday aside from Christmas— we actually get not one but two days off. I think this reflects its cultural as status as a highly important holiday, to some extent.)

In the US, Thanksgiving is also the day on which, despite increasing familial atomization (a phenomenon that affects white families especially acutely), families are most likely to meet and feast together so that extended relatives actually see each other in person. This is where you get the talk of 'when you see your family at the Thanksgiving table this year', and so on.