Small lakes in swamps to liven up the swamp from just "weird tree's"
"More rocky hills, and less smooth hills: more interesting hills would be nice.
"More lively Mountains": Instead of just those round rocks atm.
Make there appear farmed fields around city edges, on green grasslands that simulate people making foods.
Cities located near rivers should make some tiny fishing huts pop forth near the river, just as background mesh.
Hunters lodge's in/near forests located near cities.
Of course as said by "Stupidity10", make snow landscape near the top and bottom edge of the map:
Different kinds of forests: Just to lively up the current forests, which get bothersome in the amounts of the map they cover. Make it so the editor recognizes which forest is which, and then cover that forest with a given tree sort.
More lush grash, meaby 2-3 grass textures, again make them not blend into each other, but vary the texture depending on the climate or zone.
Also if you work on your generator to make sanddunes larger but less of them, make water a littlebit more... opportunistic creating big water walls (the one splitting europe and afrika for example)
Also try making the map generator create more "regions", meaby put some small feature in certain regions (more bears in one region). Unless that is too much of a hazzle ofcourse .
All these should be considered ideas.