I've played pretty much every MMO to come out, and they all have one thing in common (at least for me).
They're the most fun when they are young. (Ok, that sounds a little perverted). But what I mean is that after a while, the bulk of the players are so experienced and jaded that they leach the sense of wonder and discovery out of the game. They know the optimal ways to do everything, they know where everything is, all the tricks and exploits, etc. When a game is first released, you stand a much better chance of playing with people that are discovering it for the first time along with you. Much harder and less 'efficient' but a darn sight more fun.
DDO was the same way, but the nature of the game caused that sense of wonder to wear off a little quicker, for me. It was an absolute blast early on. One night, Wulf Ratbane and I were exploring a fairly long dungeon that was designed for a full party. We were in over our heads, but through caution and good tactics, we managed to prevail over the course of several hours. It was absolutely some of the most fun I've ever had in an RPG, computer or otherwise. The underground realm felt real and spooky, and the constant threat of death kept the tension higher than usual for a computer game. Fast forward a few weeks, and we're zooming through that same dungeon at light speed. DDO pretty much required you to repeat quests several times to get enough XP to level. That's gotten better with the addition of new content, but still a problem.
DDO can be a lot of fun if you can get a few people that haven't played before to group up with you and play it as a party. But at this point, if you start by yourself, you're going to be grouping with people that are starting their fifth or sixth character, and who know everything by heart. Unless they are ready to indulge a newbie and let you discover things at a normal pace, you'll likely find yourself zerging through stuff so fast you don't get to really have fun. In addition, at most levels there are going to be some quests that are just better than others in terms of reward (XP, loot, or both). Those quests you'll always be able to find people to play with, but some of the 'weaker' quests you may never get to do, as its hard to find groups to run them with, and you eventually level past the point where you want to do that quest at all.
Be aware, too, that nearly all MMOs require a hefty time commitment to get the most out of them, and that most are poorly suited to solo play. Look around, though, because most of them that have been out for a while have free trial offers that will let you taste a bit before buying, and that will also let you see if your PC and internet connection are up to the task, as these games can be quite demanding.
