I liked Nightfall a lot as the graphics reminded me of Pre in the quality of execution.
I really liked the customizable skill bars and equipment for the heroes and the ability to direct them in battle. Being able to setup Koss as a W/Mo with Mending and Gladiator's Defense and send him in to tank was pretty cool. Clearly though, wanting to equip all my heroes with the best Greens will be a challenge - I am currently gathering a horde of Collector's items for them in anticipation.
It did not seem as much a grind to me how they combined advancing one's character with advancing in rank - much better than faction farming in Factions.
Bottom line for me is that Nightfall looks like a winner.
(Never played WoW but looking for a screenshot when you hit 60

)