The Elder Scrolls series rose to immense popularity after the release of The Elder Scrolls V: Skyrim. The series' focus on exploring the fantasy world of Tamriel appeals to a huge range of gamers and introduces many more to the series's previous games. The Elder Scrolls IV: Oblivion and The Elder Scrolls III: Morrowind tend to be cited as some strong fan favorites for a wide range of reasons, along with Skyrim.
With five games total in the series and a sixth in development, RPG fans who haven't tried the Elder Scrolls games may not know where to start. In truth, Morrowind, Oblivion and Skyrim appeal to three distinct groups of RPG fans. The first two games in the Elder Scrolls series, Arena and Daggerfall are certainly worth noting as well, though they tend to be cited as skippable by long-time Elder Scrolls fans.
However, if there were one Elder Scrolls game that would be the best entry-level game for the series, it'd probably have to be Skyrim. The fifth Elder Scrolls game was a defining entry for the series, capitalizing on the popularity ganged with Oblivion. Skyrim may not be the best game in the series, but it serves as a great way to introduce new fans to the games' general formula whilst highlighting their main appeals.
Skyrim does a great job outlining the Elder Scrolls games' general premise, especially when the DLC is considered as well. This premise tends to be that a particular region in Tamriel has begun to or will face a great tragedy that corresponds with a prophecy dictated in one of the legendary Elder Scrolls. In Skyrim's case, the Dragon Elder Scroll foretold Alduin's return to Skyrim and included information that would eventually be vital to his defeat.
This version of the storyline formula used in The Elder Scrolls games is probably the most clear-cut, with a very tangible and understandable threat. Oblivion and Morrowind don't actually feature an Elder Scroll as part of their main quests, though the idea of a great tragedy afflicting a region is still present. Skyrim's use of the Elder Scroll in its main plot helps players to better understand the kind of scale that the Elder Scrolls games go for with their storylines.
Skyrim's simplistic gameplay is another reason why it works as a great starting point, though many also cite it as a reason why the other games in the series are better. In short, Skyrim's combat and spell mechanics are much more straight-forward than they were in previous titles, especially Morrowind. One of the biggest changes comes with hitting enemies, as Skyrim goes off whether the player actually hit an enemy with their attack, rather than using Morrowind's dice-based chance to hit system.
This brings up another point regarding Skyrim's simplicity. Skyrim's RPG mechanics cut away some of the extra fluff that existed in earlier games to try and streamline the RPG aspects of the game. Of course, Oblivion and Morrowind provide a much more in-depth experience, which would be better suited for long-time RPG fans. Skyrim still provides a decent amount of complexity for things like character stats, which is enough to know if that's something someone wants out of their RPG games.
Of course, Skyrim is an incredibly customizable game that can be modded into almost any kind of gameplay experience. Mods can be installed to increase the difficulty, add brand new content, expand on the character creation and even introduce brand new ways to play the game. Skyrim is also the most modern of the three Elder Scrolls games mentioned, so it'll involve the least amount of work to get running on a newer system likely.
Skyrim's gameplay as a whole is a great way for someone to see if the more complex entries in the series are for them. If someone doesn't enjoy the gameplay and plot of Skyrim, then they may not be able to find enjoyment out of the later titles. If they enjoy the game but find an issue with the game's simplicity, they may want to try Morrowind instead. Oblivion could also serve as a good second game in the series to play, as it's sort of like the midway point between Morrowind and Skyrim.