Based on 3.5 Ed, DDO is a decent, instance based MMO. Everything is a dungeon; all exp comes from quests/finishing dungeons (one cannot simply grind mobs for exp). Because it's instance based, there is no PKing and no griefing. PvP isn't all it's cracked up to be - this game is, in my opinion, mostly a PvE MMO. One can solo the dungeons (although this is tough with a wizard/sorcerer), although getting a balanced party makes playing through them on the "elite" difficulty setting go much more smoothly
A free player can get to the same max. level as a paying player (level 20). Everything is available to one who simply wishes to grind, although buying all of the adventure packs simply by grinding would probably take a couple years.
If you like MMOs and you play (or have played/liked) D&D, I suggest you check it out.
