I think you're always going to have problems with the hills/mountains and probably every other 'Miles And Miles Of Bloody Uberwald" lining up (if it aint orthagonally, it'd be diagonally, like the illusion you get looking over a large WW1 wargraves cemetary). Although you
seem, actually, to have done a good job with all the trees except the orchardy/lollipop ones. Not sure at first glance if that's due to a variety of alternate tiles dithered around (pseudorandomly or cued by the tile data) ?and/?or you've actually just well-dithered by offset a single or small numbers of template tile suited for that map-spot.
But whatever you do with the firs (in particular) definitely needs applying to the mountains. The hills look vertically dithered but stand in otherwise orderly columns. There's a
trend towards columns in the firs but it's broken up by conspicuous offsets, whatever the cause.
I'd be cautious about taking 2x2 cells (alike in nature) and putting
a 4-cell image in there, at least not compulsively, as it'd just make a bigger pattern obvious with "foothills" in all the unreplacable edge/tweeny gaps. Unless you are willing to go further than 2x2 in size and thus allow for some of the better
Apollonian packing or Crazy Paving effects. i.e. the RHS of
this instead of the LHS. Or approximate it by a Penrose tiling (yes, I know you've got a checkerboard grid to work around, not saying it'll be easy!) avoiding the "still
looks regular even though it actually has no symmetries" pitfall.
No, that's just going beyond your brief. Pseudorandomly dithered displacements or a large(ish) selection of alternate-but-equivalent images (like vanilla non-uniform grass from a subset of simple punctuation marks) is probably your best bet.
And that's my "you wanted a critique, and that's my critique" bit over. I like it in most other aspects and no other problem arises that hasn't already been mentioned (maybe more adamantly than I would have personally committed to, in some cases) so that just leaves me wanting to say I like the general look. Perhaps a tad less saturation
might work well across the whole thing, but just like Tolkien's line-drawn maps aren't intended to have 1:1 definition of the actual land, you can only do so much with the platform you're working with. And even then it looks like you're eking out more than you might have been left with.