I noticed a few people listed games from The Elder Scrolls series in their top 10 lists and thought it would be interesting to create a topic to discuss Bethesda games in general. The nice thing about Bethesda games is they generally take place in a sandbox; there’s no requirement to follow the main quest, you can just go and do what you want. That can also be a detriment; the lack of direction can make them feel more like a set of tools than a “complete” experience. A bit like fighting games in that regard.
I recently starting playing both Skyrim and Fallout 4.
Regarding the Elder Scrolls, I tend to agree with @frelled that Skyrim is the peak of the series. The world of Skyrim is quite immersive and diverse, plus the gameplay has been refined a lot. I can actually see myself putting a decent amount of time into Skyrim, even if I don’t complete the main quest. I tried both Morrowind and Oblivion back when they were released, but didn’t get heavily into either of them. I liked the combat in Oblivion, but found the world too repetitive, and lost interest. Morrowind was more immersive, but was let down by some of the more “clunky” gameplay elements. I’d be interested in revisiting the world of Morrowind, which I might do depending on how Skywind turns out.
I bought Fallout 4 because I wanted to play a new release, high production title that would push my hardware to the limit, but without having to commit myself to a lengthy gameplay experience. Fallout 4 was actually my first Fallout game. It obviously looks good, but the world feels quite immersive and diverse too. The addition a Mass Effect-style dialogue choices is nice, even if they’re often not very consequential and lack the depth of more story driven RPGs. I like how there’s normally an option to be sarcastic to NPCs who they try to send me on fetch quests. 
There’s also the option to have a companion follow and aid you on quests, and this provides room for more personal dialogue options to unfold. I can’t comment on previous Fallout games, but the dialogue system certainly feels like a step up from any of the Elder Scrolls games.
But other aspects of Fallout 4’s gameplay do make your actions feel consequential - ammo and items are rare, there are trade offs for using items (e.g. consume particular items and you’ll increase the amount of radiation in your body). I’ve barely scratched the surface of Fallout 4’s quests, but just wandering around the world is enough to make me feel like I’m a survivor in a post-apocalyptic world. It’s a hazardous world and there’s a sense of accomplishment just crossing the map even if you’re not actively pursuing a particular quest. I think that’s what I like about this game; I feel like a part of the world, despite the lack of story or quest direction. I’m an explorer and a survivor with the freedom to do and go wherever I want to, not bound to follow a set of tasks laid out my some NPC on high, but at the same time feeling finite and vulnerable because of actual environmental constraints. Its an experience that can feel both belittling and enpowering.
It remains to be seen whether Fallout 4 or Skyrim will hold my attention all the way to the end of their main quests. But since there isn’t a “right” way to play Bethesda games, perhaps the point to take away is that this doesn’t matter. In any case, I think Bethesda games are evolving in a positive direction.