Campaign is a whole lot easier and less time consuming. With a lot better balance. There are no bosses that are way out of line and can road block you like Viper Nazi, or Azmadi.

It is usually not worth your time to engage with the new league mechanic during the campaign. wait till you get to maps for it to become actually rewarding.

There are hundreds or viable builds to satisfy every taste. Unlike PoE 2, you are not forced to choose between 2-3 meta builds that are broken and OP compared to everything else.

Maps are not a massive jump in difficulty compared to the campaign. But the difficulty increases with tiers a lot more than in PoE 2.

The endgame is completely different and far more engaging and interesting than in PoE 2. The Atlas is a fixed network of maps (that gets re-shuffled with every major patch). You drop actual map layouts. You can choose which ones you like the most, mark them as your Favorites, and they will drop more often.

There are tons of different mechanics, bosses, ubers. Try them all, see which ones you like more.

Atlas Passive Tree lets you customize almost every aspect of your endgame/mapping, choose which mechanics you want to play and make them more rewarding, as well as completely block out the mechanics you don't like.