I agree that the world generation sucks currently.
No idea how to improve it though!
Maybe hand drawing the map, at least to some level.
Or well, I have few things:
Current idea that all of the rivers are connected to each other is not good thing! I think that all of them should not be connected to each other.
For example, it makes travel by boat way too OP. Looks ugly and unrealistic.
Coastline looks stupid in many places (lakes mostly).
Cliffs are generated in a dumb way.
Some biomes are too small, there are small dots of some biome in middle of some other biome, does not make sense.
I think that saying "big masses of water are waste of space" is a stupid thing to say when we have massive mountains everywhere, taking lots of space, not being used for anything. Maybe if they were bigger, they would block movement, which would be interesting. But currently they only add two minutes more to your knarr trip....
I think there should be less rivers, but maybe some bigger ones. Small amount of really big rivers that go across the whole map.
Kind of like some posters have stated above.
First, a big and wide river, then some smaller rivers branch off it, and some smaller rivers branch off that, but then, no more rivers, then it ends.
Also, you should be unable to use larger ships such as knarr in the smaller river branches. You would have to use smaller boats on them. Knarrs would be mainly for travelling the big rivers. Maybe players could build big harbours in various points of the really wide and large rivers that cross the world.
No idea how difficult it is to generate branching rivers.

Kind of like this, but more of them.