I'm hoping for a slightly better balance in the sizes of various regions of the map, and, of course, a larger map area as well.
The thing that struck me weird in RDR was that the Great Plains and Tall Trees areas seemed a bit small, kind of like the designers did them last, and ran out of time. I loved the atmosphere of both of those places, and Rockstar tried hard to make them seem bigger by packing a lot of varation into them, but things seemed a bit too close together,
Specifically, I thought Great Plains really should be "greater." It felt more like a Great Field, just zip across it to Tall Trees.
And then, Tall Trees had a fantastic vibe, a beautiful forest, great topography, but it should have been larger, before an almost instant transition to snow.
Finally, I really loved the Cochinay snow covered mountain (singular, only one) which had a beautiful feel also, but it almost felt more like the size of a largish building, rather than a whole mountain. I hope for multiple snow-covered mountains and treacherous mountain trails in RDR2, with a more gradual transition from dense forests into snow country.
And as long as I'm complaining, Blackwater seemed pretty small, too.
TL;DR: All of this observation is in context of the seeming large sprawl of the western part of the RDR map and Mexico. The East of RDR was too compressed.