Would the United States be what it is today without slavery?

No. Slavery was central to the US economy up to the time it was abolished. Slavery was worth more than all manufacturing and railroads in the US at that time. Slave products were 3/4 of all US exports. Industrialization began with textiles from slave-grown cotton. At the same time, slavery made the Southern economically weak and less likely to use new technology.
Slavery guaranteed early US society would be based on white supremacy. Some scholars argue racism began as a way to justify slavery. Early Christian churches sanctioned enslaving non Christians. When Africans began converting to Christianity, Europeans justified slavery by claiming Africans were a separate and inferior "race." The idea of race did not exist before. It's a socially constructed fiction with no scientific basis.
Two thirds of US presidents before Lincoln were slave owners. Two of them, Jackson and Polk, were slave traders. Half the members of the Constitutional Convention were slave owners. Slavery was originally recognized and protected under the Constitution. Obviously there would have been no Civil War without slavery. The sole purpose of the Confederacy was to defend and expand slavery. Obviously the US would be quite different culturally without the 1 out of 8 Americans who are descended from slaves.