You can check the Wiki for basically all of the spoilers, it would be weird to list all the new features in one reply. But to sum it up, we have three new levels, Cold Blood where we will kill a bullfrog (and fight Little Black Ants and Head Ants), A Bridge Too Far where you will grow your population to a certain size (and also kill the Great Blue Skimmer), and FC4 which, as far as I know, we know nothing about. And in these levels, there are carnivorous plants, three new ant species, a whole bunch of enemies (I think about 15?), mechanics like titan climbing and bridge building, and of course, a beautiful environment.

TL;DR It's definitely large, at least twice as large as the leafcutter update. While it may not take longer to play through, it's quality and features are amazingly massive.