I played DDO almost exclusively before I went to ESO, have not really been interested in any other MMO's, so take this for what its worth.
no tab targeting like DDO, the "engagement" ranges on melee attacks are larger so you don't have to be attached to your target to hit them. it was an easy transition from DDO to ESO.
does not have the build diversity of DDO, but then what other game really does. 4 classes with 3 unique trees a piece, then lots of other trees available to everyone, and you get enough skill points to get everything you could want (all the armor and weapon trees, especially if you don't craft) though every class gets flashy moves so nobody gets overly jealous of one particular class, and they do all play differently.
combat and movement is very fluid and free of micro management. what I mean is because there is nothing on the screen to click your mouse is your look all the time (like holding right click in DDO constantly) and if you have a mouse with buttons on the side (I have a naga personally) you really don't have much to do, leaving you to just focus on your gameplay instead of what ability your mouse is hovering over or where you placed that clicky on your numerous hotbars.
voice acting and quests are some of the best I have encountered in MMO's period, it is very elder scrolls though so you get a lot of the same voice actors for people. I must say though when I messed with FF14 I was shocked at the lack of voice acting and realized I had been spoiled. plus the star power, I love some of the people the got to do voice acting and some are great characters in game: John Cleese, Bill Nighy, Kate Beckinsale, Alfred Molina, Michael Gambon. plus some others, you may recognize voices from mass effect and ghost in the shell.
Graphics are good for an MMO, the lighting is very nice as well, I have often just /walked across the world enjoying the views. All the various forms of armor are pretty cool looking as well, there are some tricks (painted on depth instead of real depth and tassets and other pieces of armor floating around) but it all still does look good and was kind of required to have so many people and so much stuff on the screen at once and still look good. (and it does, you can tell what people are wearing from a distance PvP while you sit up on a keep wall sniping them from a safe distance)
PVP is awesome, when you get into one of the 100s vs 100s keep sieges it is very fun, though often its pretty one side. and you will spend a lot of time on a horse after you die or wipe because the map is so damn big. though there is a pretty large skill gap, some people will rape face, others will get there face raped.
Grouping is fairly non existent, no lfm panel, bad lfg tool, only a few instanced dungeons, literally the biggest failing of ESO and I wish they would focus on fixing it, but I think there too focused on having no tabs or screens to click through to make a good system. Trials (raids) are okay but there is not a terrible need to run them as I will explain.
Gear, this is the reason. In DDO the best gear is usually the newest raid gear, in ESO if you invest in crafting you can usually craft a comparable set of gear for any character. that can be good or bad depending on how you feel about it, Trial gear does look badass though.
Difficulty, hit or miss. you will either stomp content or get stomped, its a very small range of "just right". and unlike in DDO where one person that is fucking epic and badass can self heal, grab everyone stones, sprint away, rez them, then lead them to glorious victory in an epic scene. in ESO you all die and wipe or win without much variation. most trial bosses have mechanics that wipe the group if you take too long so its a very pass / fail difficulty.
Company, Zenimax actually has developers, and money, and has tried very hard to listen to the players and fix things. plus they utilize the test server, they have patched the forthcoming update 4 times on the test server (bug fixes and player requested changes) before they are moving it to live. unlike DDO that just does not seem to give a crap, Lamma land is a preview server not a test server.
well there is that wall of text, though the only opinion that matters is yours. do research, watch videos, try it, if you don't like it don't play it. there are things I like about DDO still, but ESO is my main MMO of choice atm.