It's hard to fall into a comparison, as it just is two totally different things to me. That being said, DDO is a great game (coming from a tabletop freak). it allows fantastic customization of your character (over and over and over again with TR's). The crafting is extensive and very helpful for truly getting the "right" piece of gear, and contrary to what someone said....it is soloable (not sure why you want to primarily solo in an MMO but hey goferit) All dungeons have difficulty levels that the player sets so all content is achievable. *edit* this is wrong, I forgot there are many dungeons that require someone to "throw a lever" for you so you can get through a door. But this is not the majority.
The downside: Due to the FTP model, the majority of the content has to be purchased or a sub is needed. Good luck getting to 20+ with F2P content...there is not enough XP to get you up there multiple times (TR's). And the sheer amount of repetition can drive a person mad. Crafting will also take a MAJOR investment of Coin, Time (farming), and the crafting itself is VERY choppy (lag in the halls). Just remember....the game is kept alive with a skeleton crew and bugs do not get addressed promptly (like the ladder bug). There is also a large lack of replay value in much of the content, and you are doomed to repeat EVERYTHING.
All in all, its a great game to kill some time, the repetition will drive most players to take long breaks from the game though.
With all this being said, even though ESO hasn't launched yet, the crafting is REALLY awesome. The ability to customize gear, to learn unique recipes, is such a lure. IT makes your character unique to you (for the time being) Its not a cookie cutter crafting system, which is important to me. IT has a similar immersion value with all of the books and lore that TES provided (much like DnD), and characters can be customized very well.
ESO is P2P which is how they all start, and personally I hope it stays this way. Just seems people fail when the F2P model is adopted and content begins to fail....ESO has a lot of content and I hope it continually turns out for all members to enjoy...a subscription is a low price to ask in my opinion.
After 10 years, DDO has playability....I call that success.
ESO has a massive fan base behind it, a great history, and the BETA's have been amazing (minus the beta bugs and the constant stress tests LOL but that's why we are there)....it has the promise of being a truly awe inspiring game that will keep us hooked. Let's hope so!!