I've played a lot of MMOs and I've played a lot of DDO and I can say I've never seen anything quite as ridiculous as the amount of lag players are forced to deal with in some raids. I would say a good 25% of the raids that I take part in are significantly effected by bad server lag and about half of those result in lag so bad that they cause raid wipes and failures. I'm not even saying that it makes some hard encounters harder, it makes it so that an encounter that could be 4 maned wipes a full raid without anyone being able to do anything about it.
This needs to stop, for years I've been trying to get other gaming friends of mine to come and play this game and as soon as they hit end game and see some of the ridiculously laggy raids they lose interest. This stuff needs to stop.
So my suggestion is that the devs need to stop doing anything new and fix this problem because basically all the new content in the world is useless if 1/4 of the time it's so laggy that it's unplayable.