The Dungeon Master. The narration helps me immerse myself in the game world. (This may seem like a small detail, but it adds a lot to my enjoyment of the game).
Repeatable Quests. I can replay any quest as many times as I like and still get XP and loot.
Variable Difficulty. Quests have five levels of difficulty to choose from: casual, normal, hard, elite, and epic. (Note you have to unlock the last three. If you beat hard, you unlock elite, etc.) This makes leveling easy and adds new life to old quests.
Hirelings. Are you a caster without a tank? No healer in the party? You can just spend a few coins and get a hireling of nearly any class/race combo.The hireling stays with you for the entire dungeon. (I pay one fifteen gold and hire a cleric and the two of us can easily complete dungeons on the hard setting)
Puzzles. For those that tire of hack and slash, DDO includes many challenging puzzles into some quests. (I tried some out this weekend and was greatly impressed)
It’s D20 system. DDO uses 3.5 mechanics (modified slightly for video game use of course). I like the familiarity and ease this brings. It also makes character creation a snap.
It’s Free. DDO is completely free to download and play. Granted there are options not available to the free account players (namely the Favored Soul class, and some races: drow, half orcs, and warforged). Also, free accounts can only have two characters. Wizards makes their money through the DDO Store, in which you can spend money to get points which can be used to buy several things (items, classes, races rare adventures, hirelings, etc).
DDO is certainly worth a try. I am enjoying it greatly.
DDO concept art from Wizards.com
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