Player made missions -- pretty neat. I tried one last night (you talk to a Harper agent and 'follow up on a rumor'), and it turned out to be a multi-map deal with unique(ly named) enemies, triggered traps used to make a puzzle, and a multi-step questline.
How D+D is it? Well, it's 4Eish in that you have 'encounter' powers (with a cooldown long enough that you *might* use them 2-3 times in a long fight) and 'daily' powers (with a much much longer cooldown based on 'action points' that you'll use once or twice per map) but mostly rely on your at-wills. That's about it, really, mechanics-wise.
That said, the combat is awfully fun, at least playing a 'control wizard'. I don't have CoH levels of control, but I do get to actually hold people and then beat up on them while they're frozen statues. And you're usually fighting small groups of enemies instead of single tough monsters. AND because of the way health recovery works (it doesn't recover), there's a lot of give in the difficulty level if you're willing to chug health potions, since you're expected to get through each fight with minimal damage.
Worst thing so far: voiced over cutscenes. The mouths move but NOTHING ELSE and it looks SO CREEPY.