I know they are made by the same developer. Doesn't mean the worlds are the same. Fallout 3 and Skyrim are different.
Tell me, what is the major element of Skyrim? Go into a dungeon, slay a bunch of draugr and get out with the loot. That's the core of Skyrim experience. You can add some flavor to it, by undertaking a quest that gives you a reason to do so other than basic greed or curiousity or by coming up with roleplay ideas. I highly disagree with your statement that each of 150+ dungeons gives you unique experience. Few dungeons have those notes and backstories that make exploring them interesting. A lot of them are just generic kill zones.
I didn't find anything amazing or incredible in vanilla Skyrim quests. The only one that can stand up to a Bioware story is the Dawnguard IMO, with Serana who's the most fleshed-out character in the game and comes close to a Bioware companion.
Where Skyrim wins is the freedom it gives to the player. You can do almost anything you want, you're not bounded by quests, you can even chop wood all day if that's your idea of fun. Your character is a blank state and stays that way throughout the game. There is no personality, other than what you can come up with. ME won't go that route.
World and franchise are irrelevant. They have the same core design, which is the point.
That's the major element you got out of Skyrim? You are way off the mark. I'll tell you what Skyrim actually is: An experience where you can go wherever you want and do whatever you want. That's Skyrim, Oblivion, Fallout 3, Morrowind, and every BGS game in a nut shell. They make games they want to play, and build worlds they can get lost in. My point about their dungeon crawling activities with the 150 dungeons is just one of many things you can do in the game. This is a far better alternative than the cookie cutter fetch quests of most open world games. There is a reason every single BGS game has been GotY for the past 12 years, I assure you...
Every single dungeon in Skyrim is hand-crafted and is unique (the work of eight dungeon designers). This was not the case in Oblivion, which had well over 300 dungeons, and most were cookie cutter and identical (the work of one dungeon designer). Whether you appreciated the time and effort is merely subjective, and does not take away from BGS' achievement. Most of the guild quests (besides College of Winterhold) and all of the story DLC (Dawnguard and Dragonborn) were all extremely well-executed and high qualtiy. This is no surprise as BGS has been doing award-winning DLC since Bloodmoon, Tribunal, Knights of the Nine, and the Shivering Isles.
I never one stated MENext was going to be Skyrim. What I did say is BioWare is taking a lot of those open world ideas and incorporating it into their games. Look at Dragon Age Inquisition. Dr. Ray Muzyka even stated after Skyrim released that it was going to have a major impact on Dragon Age Inquisition's development. The point is BioWare games, going forward, are making a focus on exploration-based content and plenty of activities to find. Also, our character will be a "blank slate" in MENext, as the player will build the protagonist into a hero, rather than the protagonist already being a hero like Shepard.