It's like the fullest blossoming of 1990s nostalgia! I bought into the Valiant universe in a big way back in those days. I had every issue of every single title. In fact, I'm pretty sure I still have them, bagged and boxed at my mom's house. Written by Jim Shooter, Harbinger featured some nice art by David Lapham; while in tone and general look it owed a debt to Chris Claremont and Brent Anderson's X-Men: God Loves, Man Kills graphic novel (which Neal Adams claims Shooter conceived), it prefigured the more comical Gen13 and Marvel's Runaways-- and stands as the best thing Shooter's finest scripting hour, Secret Wars included.
Pete Stanchek, the group's leader, wasn't exactly the most trustworthy of people with his powers of mental control. The intimations that he'd occasionally use it for his own convenience and the implications that has for all his personal relationships made him seem a bit shady despite his frequent protestations of remorse. I was never sure if I even liked him.
Harbinger was also notable at the time for the "play for keeps" nature of the superhero fights. People got hurt-- and badly. Or killed outright. Very different from the low stakes dust-ups in most superhero books at the time. I mean, face it, Wolverine might kill a few ninjas here or there and Katana would SHAKKT someone off-panel, but killing fights in comics were pretty rare. Deaths usually happened to supporting characters to motivate protagonists. Even battles with actual consequences were rare at the time Harbinger came out. No broken, bloody noses for Batman, and only Dani Moonstar had to endure months of painful physical therapy for her injuries-- very little of which we actually saw. Of course, nowadays Katana kills practically in every issue of Birds of Prey and no one says boo about it. Books like The Punisher and Kick-Ass play gory injuries as jokes or as really cool, lots of fun for everyone involved. Spend some hospital time, pop out good as new, join in lopping off people's heads in full bloody color for kicks and giggles. In Harbinger, they were just disturbing. And apparently, Shooter had even more areas to explore with Stanchek.
I also really enjoyed mismatched buddy comedy Archer & Armstrong and their darker take on the old Gold Key series Solar, Man of the Atom. It's too bad Solar and his fellow Gold Key alum Magnus (the guy who, like the Flaming Lips' Yoshimi, fights evil-natured robots) won't be part of this revival; they're over at Dark Horse.
Even though I've gushed here about Harbinger, Valiant's actually kicking off with X-O Manowar this time. I read that one but to be honest, I have very few memories of it.