According to Phil Spencer, Microsoft's upcoming Xbox Series X will deliver 12 teraflops of graphics processing power, or in other words "twice that of an Xbox One X and more than eight times the original Xbox One." This confirms rumors from December of 2019 which suggested the next-gen specs would more than double Xbox One X in a lot of areas.
Teraflops, if you've forgotten (and we wouldn't blame you), are used to measure the power of a GPU. They are calculated using the core count and clock speed of a processor.
More teraflops doesn't always necessarily lead to better performance in practice, but with two to eight times that of the last console, it's pretty safe to say the Xbox Series X will be a big improvement.
With such fast next-gen consoles, your reaction times are going to play a more substantial role than ever before.