It looks nice. Better than WoW IMO - WoW captured the LotR style colossal statues, massive waterfalls and alike, but everything came across to me a slightly cartoony. DDO looks crisp & clean. Armour looks fantastic... Better than WoW's 1980's style shoulderpads!...
Quests in DDO have 4 difficulties on average (Solo, Normal, Hard & Elite) allowing for re-playability, and each step is usually quite a significant one. Again, the quests range from quick ones that take only 2 minutes, to ones that'll keep you busy for at least an hour.
Combat. WoW doesn't have combat. You click a button and wait. I think a lot of WoW's success is due to it's combat system's compatibility with people - it's so easy it's, well like I said, pretty non-existant. DDO involves at least a little skill. Even catching those Kobold Shamans is tricky! You're having to move, swing & use spells, feats, skills and items at the same time. YOU actually feel as though you've done something, not just let the computer do it. (For those who defend WoW's combat -would you play a fighting game -Tekken say - if all you had to do is select your enemy and click 'attack'?
Levelling - DDO takes a long while to level. Each level has 5 sub levels. It CAN be a long process, depending on play-style & how much time you invest. I believe WoW was easier to level in - actually I know it was. It took less than a few days to rank up to level 6... My highest level DDO character is level 6 now. I have had the game since release - AND hated it. I literally got bored about a month ago and gave it another go - and was shocked my how much it has improved!!
DDO's downside it grouping - and for me, stormreach's layout. Travelling from area to area can be quite a mission, the city is a maze and is easy to get lost in - and due to this you can have a 15 minute wait on your hands before everyone gets to the mission. There also seems to be lots of high & low level players about, but few mid. If you want to be popular - make a cleric... There is a lack of them, and a party heavily relies on one.
HUD is simple enough. Auction house I only buy from, not sell - I'm lazy! Farming doesn't really exist that much in DDO, not to the extent of WoW anyway. DDO is a lot more based on the fact you're AN ADVENTURER, NOT A CRAFTSMAN!
I think DDO has a much more solid foundation (from the PnP) as well as a lot more options available in the future. Remember WoW was based of a basic pc game (how many different classes/unit types? - compaired to D&D's 'OFFICIAL' 170 something classes and thousands of monsters! DDO is based on a very indepth & detailed game with hundreds of rules, feats, skills, magics etc, etc. So in theory, if they got it all balanced and all included, it'd be truely a mind-blowing game. But until then, we'll have to wait!