This comic series won’t have lasted long, indeed the Darth Vader series is ending this August with the issue 25 (the last volume combining the issues will be released in November). The story took place between A New Hope and Empire Strikes Back, an era that Marvel seems to exploit too much while Star Wars is such a rich universe where there are plenty eras to explore so maybe this will open the door for a series set in another era.
This is what Kieron Gillen the writer of the series told IGN
“…we kind of looked where we were after Vader Down, and we realized we were probably actually nearer to the end than we thought we were. And it was a situation where we were like, “Okay, it’s better to actually end this story in a way which we think is the most effective. We don’t want to pad it out extraneously.” That was the kind of thing, we were like, “Oh yeah, this is the end of this particular story,” in which case it’s a natural place for Vader to move on…”