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That being: Daggerfall, Morrowind, Oblivion, Fallout 3 and Skyrim
I think there have been some games between Daggerfall and Morrowind? Or before Daggerfall?...but you get the idea. New Vegas however does not count, because that was not made by Bethesda.
My favorites are Oblivion and Skyrim, with Fallout 3 going to a distant third.
I still play Oblivion, and the modding community has matured a lot with it...still quite a few mods for it, and still quite a few people play it. Its different enough than Skyrim, that one can (in my opinion) technically play both and enjoy them for different reasons. I might favor Oblivion a bit more, because the mods are more mature...but not just that...the game seems to...well...have more character development aspects to it.
Skyrim however is still great, but a lot of features were taken out. Oblivion the same, with taken a lot out of Morrowind, but personally, could never get into it. I didn't like the world, and the NPCs were all static and that kinda ruins it for me. And I just never liked the look of Morrowind. But for its time, I'm sure it was great. I kinda missed out on it is the thing. I know there is the graphics overhaul mod for it that makes the graphics look WAY better, but just can't get into it. The graphics were never really a problem for me in games.
But Skyrim is AMAZING for taking screenshots, especially when modded...the game looks just beautiful. And the main story is better than doing the same Oblivion gates over and over. The sidequests are good...except for Oblivion Dark Brotherhood, Thieves Guild, blow any of that out of the water. Especially the Brotherhood, the best quest like I've personally done in a game. or at least up there. Forgot what the mage and warrior guilds were like in Oblivion...I'll have to do them again.
As for Fallout 3, I had a lot of fun with it. The story never caught on with me, but I enjoyed playing in the world and doing the side quests. I don't play it anymore, but I played as many hours as I have Skyrim...which while I still have many hours left in Skyrim, it was still quite a lot of time played.
My Skyrim, Fallout 4, Starbound and WoW + other game mods at MODDB: