Jody Macgregor (PC Gamer) tells the history/evolution of the Elder Scrolls series:

The evolution of The Elder Scrolls

There’s a theory that no one ever loves one of Bethesda’s open-world games as much as they love their first. Whichever of the Elder Scrolls games was your introduction to the format will be the one that sticks with you forever, the theory goes, and none of the others will measure up. But although there certainly is a format shared by all the single-player RPGs in the Elder Scrolls series, there isn’t a formula–each new game makes significant changes, and many of those changes seem like responses to common criticisms of the previous one. It feels like Bethesda pays attention to the things people complain about and use mods to fix, though the company rarely gets credit for it. It’s especially noticeable when you put all five central games in the series—ignoring the spin-offs—side by side to see how they’ve evolved, and how different they are. We'll follow that path now, starting with The Elder Scrolls: Arena. [...]