That is about spot on what I was thinking in regards to the way it should look, and I have even tossed out a little futher thought on this (though not per se through looking into Argonia lore much for area descriptions).
I have always pictured the eastern coast as being something akin to marshes tapering into some low flatlands on the coast with some light foresting mixed into it:
http://i5.photobucket.com/albums/y176/RedEye_tha_Harvester/morrowind/argonia_eastcoast_001.jpg?t=1256634206
On the southern coast, I kind of always pictured that the inland swamps would have the strongest pull leading to the south, and it would still remain a very thick swamp, with patches of open marshes mixed in:
http://i5.photobucket.com/albums/y176/RedEye_tha_Harvester/morrowind/argonia_southcoast_001.jpg?t=1256634025
On the northern border to Morrowind, I always imagined the various mountains and forests opening into a thin and cracked type bog, like small islands broken by little rivers all over:
http://i5.photobucket.com/albums/y176/RedEye_tha_Harvester/morrowind/argonia_northborder_001.jpg?t=1256633928
At the western borders with Cyrodiil, I had pictured a more spread out bog land, as though a flat land had been dotted by many small lakes all over the place, constantly impeding ones path:
http://i5.photobucket.com/albums/y176/RedEye_tha_Harvester/morrowind/argonia_westborder_001.jpg?t=1256634123
Due to the nature of how I pictured the eastern coastal area, I imagined that the eastern midlands would actually be rather plesant, as the forested coastal marshes open into an open plane of flower laden marsh land:
http://i5.photobucket.com/albums/y176/RedEye_tha_Harvester/morrowind/argonia_eastmidland_001.jpg?t=1256633746
As for the midlands to the south, since the coast region I pictured will still fairly heavy marsh and swamp land, I imagined the southern midlands to be increasingly dense swamp forests:
http://i5.photobucket.com/albums/y176/RedEye_tha_Harvester/morrowind/argonia_southmidland_001.jpg?t=1256634079
The midlands of both the north and the west would be fairly similar, due to the similar border construction - both opening into much larger and deeper open marsh lands:
http://i5.photobucket.com/albums/y176/RedEye_tha_Harvester/morrowind/argonia_northmidland_001.jpg?t=1256633968
http://i5.photobucket.com/albums/y176/RedEye_tha_Harvester/morrowind/argonia_westmidland_001.jpg?t=1256634165
Once you finally made it to the inland area of Black Marsh, regardless of the direction you came from, you would find yourself in a deep and dense swamp that consumes all of the heartland of the province:
http://i5.photobucket.com/albums/y176/RedEye_tha_Harvester/morrowind/argonia_inland_001.jpg?t=1256633820
http://i5.photobucket.com/albums/y176/RedEye_tha_Harvester/morrowind/argonia_inland_002.jpg?t=1256633859
http://i5.photobucket.com/albums/y176/RedEye_tha_Harvester/morrowind/argonia_inland_003.jpg?t=1256633898
Anyways, that has always just been my personal take on it, I know zackg has done some extensive research into lore for this, so I trust the development on that aspect.
Either way, hope the pictures and ideas help