Hubble saw everything in the visible part of the spectrum which was amazing. Lots of new discoveries with Hubble.

With Webb, it viewes in the infrared which allows us to see into nebulas and galaxies. It also allows us to see very far back in time, to 350,000 years after the big bang, something we have never seen before. It'll also be great for observing exoplanets and will be able to analyze the light from lots of sources at the same time. It'll change how we see the universe. It took 20 years to develop and build this telescope, it's way more powerful than Hubble, which is an amazing telescope.