Lets see, the purpose was different, the architecture was different..
Why do people make it so black and white? If Bethesda didnt name it after TES, I know some people wouldnt make that connect and would argue about it.
Lets make a comparison on a specific scaling
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Morrowind Battle System = Based on the shear ability to just hit someone, you hit less than you miss. Blocking is a chance, and you dont even do it by yourself
Oblivion Battle System = Based on how much damage you do, you hit always unless you arent in range. Blocking is a personal skill, the limiting factor is how much damage it absorbs
Now how are these 2 similar? They are 2 different styles. Its like comparing Hard Core rock and Rap, they are different.
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Morrowind Landscape = Often you found random mountains burrowed with the always obnoxious "Cliff-Racer," seemed to me it was a lot less green than oblivion, most of the land had Daedra everywhere (In comparison to Oblivion there are only daedra in select locations and in Oblivion Gates)
Oblivion Landscape = The Mountains were only in select locations where they would be apparent, a lot more green, grass and such.
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Morrowind Architecture = Mostly Dunmer, with the exception of certain imperial cities. A lot of Daedric Shrines everywhere, almost always yellow?
Oblivion Architecture = Varied based on location, Bruma had a bit of Colovian and Nibenese, the Imperial City was Ayleid, And the others were either Nibenese or Colovian
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Morrowind PC Setting = A man released out of jail messaged by a Daedric Lord named Azura, to be the said "Nerevarine"
Oblivion PC Setting = A man broken out of jail on favor of the Emperor. Who was only told to give an amulet to someone.
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Morrowind Setting = Morrowind
Oblivion Setting = Cyrodill
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Now, lets say Oblivion and Morrowind took out any hints that they were connected, and they werent named by the same franchise.
How are they similar? They are 2 very different games about 2 very different things in 2 very different places.
You are trying to compare games based on their connection to eachother, not the actual gameplay
If anyone can find me 2 big similarities other than the TES franchise and "both in tamriel"
Then bravo.