Try it out you will know within a hour of free play if it is for you.
I have become hooked on DDO and have brought about 7 others to the game. Turbine has created a great interpretation of Dungeons and Dragons rules set. Sure as an old Pen and Paper player I could quibble but really there isn't too much to critize about DDO. Compared to the others I have played such as WOW, Warhammer, Fallen Earth and Age of Conan it has some great features that for me make this a much more fun than the other to play.
What makes it different:
DDO is different from most other MMORPGs in a number of ways.
1) The most important is that there really isn't any significant travel time to and from zones. I personally found that to be a real chore.
2) The second is that everything is instanced so there isn't any waiting around for something to respawn because someone has just killed it.
3) As it is D&D and the skill versus difficulty challenge (DC) to succeed/fail is well established, then it is relatively easy to determine the benefit to your character of items, the bonuses they give etc.
4) Have to work cooperatively, while some say there is solo play that is really only at the low levels. Once you hit about level 6 you really need to play with others and generally most of the people playing are fun to play with even in pick up groups (PUGS).
5) Dungeons are fun the first dozen times you go through them and are generally well thought out.
6) Micro transactions have been set so that you don't really get any huge advantage over your rivals. This means that there isn't any pay to succeed in the game. I personally have spent about $70 over 6 months and that is mostly on new dungeons. So far I think this model is well done.
No Generalists:
If you go on the forums in DDO you will see a lot of character builds and a lot of comments about how doing something or other gimped the character. DDO with a lot of the higher level content design has made it mandatory to have a party of specialists to succeed. The way the have set the difficulty challenges means that unless you have a very high number your attacks, saves etc will fail too often and your party's progress and chance of success will suffer. You also need a variety of specialized gear to have success. Personally I prefer more of a generalist build and wish this wasn't the way it is. I suspect that as they have added content, they have had to go this route to not unbalance the entire game.
Item Drops:
Like many other MMO's you do tend to spend a bit of time farming dungeons for those rare drops. I personally have done this for an item or two
Improvements:
1) Dungeons could be a little more random (like where traps are set etc) to keep them fresh
2) Wandering monsters could throw in a new challenge
3) High level monsters have better AI (I know this a tough one) rather than just insane hitpoints
Summary:
If you have never tried a MMORPG then this is a great one to try. If you are experienced with them and like what I have laid out is well done with the game go for it. Really it is a lot of fun to play.