After spending Sunday evening on Doomwalker and getting the fight down pretty well, we came back in tonight and got him on our second serious attempt. Really it's not all that hard of a fight, kind of a blend of C'Thun and Sartura. Doomwalker however implements everyone's favorite outdoor raid boss mechanic: Mark of *; in this case, Mark of Death. If you get within about 100 yards of Doomwalker after dying to him, you'll... die. Instantly. This makes wipe recovery much more fun than the green dragons where you'd just get stunned. Furthermore, when you die to Mark of Death, it refreshes the timer on Mark of Death.
Well done Blizzard.
Otherwise the encounter is really pretty fun, just a bit untuned. He has some unfair insta-gib moves, but they're pretty uncommon, and will kind of go away once our gear improves and allows our HP to be a bit higher. Once again it's a fight that seems to be tuned to a higher level of gear than what's actually available.