DDO (D&D Online) has come a long way since I started playing it in the early beta. They've polished it quite a bit and it's a visually appealing game, although nowhere near as pretty or colorful as WoW (World of Warcraft). Depending on your preference, this may be good or bad.
From a solo-player perspective, this game is hard... too damn hard, in fact. If you have a bunch of buddies who play, or you're fairly good at hooking up with folks you might not have a problem. But as someone who likes to adventure alone a lot... this game is damn near impossible to progress in.
Dying sucks in DDO and happens OFTEN, but fortunately you don't get penalized with XP Debt (like in CoH) and you don't have to walk all over the countryside looking for your body (like in WoW) but you will die a lot. You show back up in the inn, automagically. You'll need to hang out for a bit while you heal and recover mana (if any). Incidentally, the inn is the only place you auto-heal. You can't just hang out in a dungeon room and expect to get hit points back. (Technically this is just like "real" D&D... where it takes 8 hours to get a single hit point back without magic.)
The NPCs (non-player characters) I have encountered so far are interesting, but the world is way too scripted. All good MMORPGs need quests and "forced events" but it seems like DDO has a few too many. The beginning of the game is way too linear. Once you have gone through it with a couple of characters, you'll understand.
As a long term D&D player (25+ years) I've been waiting for this game for a long time. For now at least, I'm going to keep waiting. Maybe after the first major expansion, I'll reconsider. WoW just does too many things right for me to switch (or pay for two MMO accounts.) The D&D license, and the Eberron setting in particular, are rich with opportunities and I think there is a ton of potential with this game. It's just not there yet.