I solo'd ALL of the MotD content on EE except CITW and the first (King's Forest) chain, including all the harper content added later. I have not yet tried to solo the High Road pack. All in all, it is not easy, but my toon is built for solo play. It's only a 3rd lifer: 18 wizard, 2 monk... name of Furian. Most of the content I solo'd the obvious way... taking it slow, and controlling agro. However, here are a couple exceptions:
Belly of the Beast: I totally cheated. I achieved this by immediately killing the casters capable of casting mass death ward, then ddooring out of the arena. I then came back, stood by the arena door, and set up a macro to cast death aura every few minutes. I want afk for a long while, came back, refreshed spell points, and then went afk again. Eventually everything was dead. I did have to go into the arena a couple times to grab some agro from the back of the arena and then ddoor out, but most of the time i was afk. I let the spectators kill the snake. The end of the quest (once in the belly) was as straight forward as any other EE quest.
Reclaiming the Rift: The negative level like effect accrued by using the barrier made this difficult. My tactic was to drag things up the ramp, and then jump off the edge. Jumping off causes you to come back on the next ledge up, out of range of the bad guys. I simply killed things from up there. When there was only one monster left i would jump down and dragged it over to the barrier to kill it.
Hope that helps. Let me know if you have questions about a specific quest.