The Nether has a massive revamp and a lot more structures to explore like the Soul Forge or the Burning Arena. There are also a whole lot of biomes that you can find like a biome where you can find some Rose Quartz instead of normal Quartz. There are also a lot more mobs- For example there is a bear that hangs on the ceiling and jumps you when you are under it.
The End is the place you go after to beat the game even though there are bosses at least 9 times as hard as the Ender Dragon but anyway. The End also has a cool revamp but it's the outer islands you should see but sadly End Ships are twice as hard to find but give you a fully enchanted elytra. There are plenty of biomes to explore in this revamp of the End including a lot of new mobs that are mosty friendly but some are very aggresive. You can find a Ruined Citadel that holds the Ender Guardian and Ender Golems and are not friendly at all b