I played DDO for about a year. It was quite enjoyable. I eventually quit because my internet connection (768/128) was too slow for raids. I was actually waiting for Module 9 to come out before joining again, as I've just upgraded my internet speed.
Pros:
Active combat. You actually run around and kill things. Attacking from behind or the side (or being attacked) actually makes a difference. Very fast-paced.
Lots of dungeons/instances - you can get to almost all of them within 5 minutes or less, no matter where you start from in the world. Many areas are located far away from the main city of Stormreach, but you instantly travel to them, so you don't spend a lot of time just traveling (unlike WoW).
TONS of character customization. You have 7 or 8 character classes, races, 6 attributes (STR, DEX, etc), skill points, and enhancements. You can multi-class, which leads to lots of great combinations.
Built-in voice chat.
Reputedly, the player base is generally more mature and helpful than in other MMORPGs.
Graphically, it's a beautiful world. But you really need to leave the starter city of Stormreach to see it.
The game emphasis is on getting a group together, and then getting into the instance within a few minutes. There is minimal time wasted running just to get into an instance. Mostly anyway.
Yes, there are dragons! and giants, trolls, ogres, orcs, kobolds, gelatinous cubes, and lots of monsters I've never heard of from my old pen & paper D&D days.
There is nothing quite like casting your very first "FINGER OF DEATH!" The bestest spell evah!
Cons:
It's not Dungeons and Dragons. It's based on D&D, but don't expect it to be especially faithful to the rules (any version).
I didn't get the feeling of being in a huge world (unlike WoW).
Built-in voice chat means you get some mouthy kids sometimes. You can mute them though.
The game is pretty much all PvE. They threw in some limited PvP to shut up complainers, but it's seriously gimped IMHO.
Soloing is virtually non-existent. Grouping is essential to success, although some people enjoy the challenge of attempting to solo dungeons. I never cared for dying 20 times in a row though.
Crafting system is very limited. The developers said that they wanted to minimize grinding, but players demanded crafting, so they threw it in. From what I've seen, crafting = grinding. Hate it.
Overall, if you like fantasy settings, give this game a try.
I strongly suggest starting with a melee character (e.g. fighter, or paladin). My first character was a wizard, and they don't really start getting powerful until level 8.
