He is far more interesting today than he has been at any point in the last two decades, and I say that as someone who followed him through his Teen Titans years and into his 1990's series and beyond.
There's a reason the character found an instant appeal and gained great readers favor through the 1980s and that reason purely comes down to the fact he wasn't just another one-dimensional mercenary doing it for a job and the money like others of his kind. Deathstroke was one of the earliest such villains to gain the longterm attention and grace of a creative vision, of a writer who added a complexity and code of personal practice that others such as The Taskmaster and Cheshire lacked. In a sense you could say Frank Castle was a very similar proposition as much like Slade Wilson he is a cold hearted killer and not one you would like to be around on a personal level, yet as a spectator looking in both of these men operate on a personal code of conduct and are selective about who they target and why. If Frank Castle was seen to be so callous and reckless as to be shooting innocent pedestrians during the course of his actions he simply couldn't function with any reader sympathy or interest. And the same methodology applies to Deathstroke.
Creating a mercenary is easy in comics, making that character interesting to follow, admirable even, well that's something countless writers have tried and failed with... By consciously resetting the character of Slade Wilson to fall back in line with the characterisation set down by Marv Wolfman and George Perez Christopher Priest is acknowledging the problems with the character over the last two decades of mishandling and taking a deliberate course to reset the character back to where he was the most interesting and nuanced.
(And yes, all this being said Slade was never remotely someone to look up to. But thanks to fine writing he was somebody you could still understand.)
Case in point: The Kingpin, Norman Osborn, Lex Luthor, The Joker in The Killing Joke, etc. Deathstroke really doesn't work as an anti-hero, that's why nobody seems to remember his series from the 90's, and that's why they changed him back.