After a solid year of playing DDO my girlfriend and I canceled our VIP subscription.
Actually, no, it wasn't a solid year. That's why we canceled. At various times a DDO update would mysteriously render one or both of us unable to log in (Searching for Logon Servers 20 of 20 error).
1: The tech support was horrible. It took forever to get a response, the response was formulaic and ignored me saying what I had already done, and eventually circled back around to suggesting the same solutions that were in the reply history of the email because they kept bouncing me back and forth between idiots at the tech support center. Took me four emails to reach someone who seemed to read and write English natively. The goal seemed to be to string me along until the problem solved itself, one of my activities fixed the problem, or I left.
2: The game has no debugging tools. I couldn't figure out what was actually going wrong, at which step in the process it was having trouble. Things I did to fix the problem would sometimes work, other times not. In general, reinstalling OS and redownloading / patching the game fixed the problem - until the next time it came up. At one point I didn't play for two months because I had the problem crop up with an update the day after I wiped my machine, and I didn't want to spend another whole day wiping and reinstalling all my shit.
3: The game itself is bullshit.
3A: It can take forever to get to a quest that you want, and there are unnecessary barriers that just serve to make it take longer to travel. Why is that even important? Is running through town zones repeatedly supposed to be fun? Does Turbine actually get anything out of that?
3B: There are too many collectible things. Every new adventure pack seems to add a new set of gear you can get, but you have to collect stuff and go to a machine and use the wiki (because it's too complicated for normal humans to figure out in a reasonable amount of time). Finally when you grind enough to get your item, you have leftover ingredients that are bound to your character, taking up bank space uselessly. I eventually started throwing away most of everything.
3C: Every new major update invalidates old updates. When Cannith crafting came out it was the best thing, but two updates later nothing you could craft was anywhere near as good as the stuff dropping on normal dungeons. Green is the new purple, you could say.
3D: Some content was just stupid. You'd drop down a pit to the boss fight, start doing your thing, and die from massive damage, who knows why? When you check the wiki there's a precise and ridiculous way to do the boss fight which is not telegraphed at all during the dungeon. Who survived long enough to figure this shit out and write the wiki page?
3E: Monks did. Monks are uberpowerful and survive everything. Monks can solo content that a 4-man party of his level would have trouble with. Monks get all of the special abilities and their epic destiny is pretty damn sweet. Of course the Monk class is premium so this is a pretty clear case of P2W. Personally I have a grudge because Monks are so dumb looking. I hate playing a western RPG and seeing a guy doing backflips and punching shit with his palms and entombing monsters in jade and throwing petals everywhere. You can play a weapon-wielding Monk - but it's significantly less powerful than an unarmed Monk. Stunning Fist shouldn't be especially useful against bosses, since they're immune to most of the other special combat techniques, but Monk players would crybaby until Stunning Fist reigned supreme again.
3F: God damn 3rd edition. I don't want to spend hours staring at a wiki thinking about "builds". That is not fun for me. It's fun for some very special people, and these typically post endlessly on the DDO forum trying to squeeze a few extra DPS or resistances out of a character. You can do 3rd edition without "builds" and "character planners" but the contender Pathfinder just dug its snout deeper into that pool of shit instead of improving on the model.
3G: Almost all of those infinite possible combinations are worthless. Just play a Monk. Or a Monk "build" ...
3H: There is endgame content, but the real endgame is reincarnating and starting over - with a tiny bonus and a hefty XP penalty. This means doing the grind again and getting to endgame - and reincarnating again. A character with multiple "past lives" can be solidly more powerful than a fresh one on its first life, but this is also partially a result of the player knowledge of dungeons and loot drops, and having stashed away good stuff to use as he levels up. But this is an illusion: this endgame exists only for the truly hardcore poopsockers who are members of TR (true reincarnation) grinding guilds. One guy advocates taking 15 levels of Sorcerer, 5 of something else, and at the end using a Turbine store item to exchange levels of Sorcerer for levels of the 5-level class, so when he does his reincarnation he can get the credit for the smaller class. Then he plays through the game again in a couple months with a different 5-level minor class to reap that benefit. And why does he do this? So eventually his character will be actually literally completely maxed out. And ... I guess then you win and move on to the next MMO?
3I: Technically free to play, but 90% of the dungeon content (and hence loot) is behind pay barriers. You also need to do different dungeons to level fast, so free players get shafted into slow progression. Also about 20% of the class and race choices are premium.
My problem with DDO is that it's just barely good enough to care about. If it were worthless my reaction would be to ignore it like I do everything else that unremittingly sucks. But the dungeons are cool. I need to find an MMO where the gameplay - such as those dungeons - is awesome and also the rest of the game isn't horrible.
In the end, what made me leave was the game simply not working properly and me not wanting to spend more than the 100+ man-hours of tech work I already did trying to fix it. It's simply not worth Turbine having a skilled person do tech support for two subscribers paying $240 a year in total ($10/mo in 3-mo bundles, two accounts).