There's a lot in ESO that is sort of fans service for fans of the series. But unless you plan to spend 100s of hours exploring the five other Elder Scroll games while developing a sense of nostalgia, you might be better off using the various wikis to get some background information. But if you do, here's a list of things I noticed, while being vague enough to avoid spoilers.
Redguard
Never played it, but I do know you meet the slug like race know as the Sload in it. In AD, you can hear more about the Sload if you ask about the history of the festival in Skywatch.
Arena
One the the five companions in the main storyline shares the family name of Arena's main villain. This is also the only other game you could travel to all the zones in ESO.
Daggerfall
This game pretty much covers the same area as the Daggerfall Covenant in ESO, in particular the cities of Wayrest, Sentinal and Dagerfall. Daggerfall was much larger in terms of the area than any game before and after. It could take a month, in game, to travel around the Iliac Bay. (You can also see a certain tower out there in the bay though you can't travel to it in ESO.) So while they couldn't recreate the city of Daggerfall to the same scale, you'll see noticeable nods to the old layout from the placement of the market place to the shape of the Fighter's Guild tower. A major villain from ESO also appeared in this game and Obvlion.
Morrowind
From the alien creatures to the names of the big houses, Ebonheart Pact makes a lot of use of the lore from this game, although you can't travel to the same areas like you can with DC. (Sorry, this is the one I played the least.)
Obvlion
The PvP zone takes the center cut of this game's map. In fact the location of things and the topography of this zone is largely the same. Many of the main story line locations will be on the DC territory side, I.E Cloud Ruler Temple. The infamous Hackdirt is at the top of the AD's territory. And a comment about the goblins in Cropsford, EP territory, will be lost on you unless you really do the side quests in TES IV.
Skyrim
Half of Skyrim's map is in ESO. Being the most recent game, they use a lot of elements, especially in EP. Keep in mind, the major religious dispute of that game has no lore background in ESO as this game predates the birth and accession of Tiber Septim, aka Talos.
That should give you the briefest idea of what you would be looking for if you want to use those games to relate better to ESO. Good luck what ever you decide.
Edited by driosketch on September 27, 2014 10:51PM
Morrowind was and still is my favourite game ever.
It is really the epitome of a 'do what you want' game, you are plonked down in a village in a world and only given the barest instruction about what you need to do next if you want to follow the main quest (I actually didn't get around to finishing the main quest until about 2010, I think the game was released in 2002/3 or thereabouts - but I spent hundreds and hundreds of hours in game before then without ever doing the main quest - the world is FANTASTIC and lots of side quests and factions/guilds to join).
Although it's first person (I do feel I have to say this to avoid disappiontment from anyone expecting ESO or Skyrim style combat), the combat is not as actiony and reactive as more modern games, yes you stand and slash your sword or cast your spells but it's all dice roll to hit - I grew up with that kind of combat mechanic in games (table top games before home computers were a big thing for example) so it makes sense to me, but some people coming new to it can find that a bit frustrating as it's not true action combat, it's a mix of reaction and dice roll type thing. Also using MGE, it is very beautiful, and the unique art style of the game shines through in modern technicolor, it comes across as a very alien landscape and culture compared to most fantasy settings. And even compared to ESO. If you want to dip yourself in true Dunmer culture, n'wah, get Morrowind and take a trip to Vvardenfell....
Edited by Epona222 on September 18, 2014 3:17PM
GM - Ghost Sea Trading Co - NA PC
Epona was a Romano-Celtic goddess dating back to around 1800 to 2000 years before computer games were invented.
I would just say that as someone who played all of the TES games.. I probably averaged around 500hours in each game. To play through all of them you might not be done for a very long time. Yeah, you could just charge through the main story on each to "finish" it but then you would be missing the bulk of the TES experience.
Thanks for the responses everyone, I think I will play the main games, but only after I've played through ESOs main story on at least one character, after which I'll come back to ESO, and it will probably have been updated a lot since then.