I didn't care for Time Killer one bit at the time, Slaine being my favourite story, but I've grown to love it. As Frank says, the time travel shenanigans are right there on the first page of the Angie Kincaid-drawn first episode, and having Slaine interrupt his physical journey home to head off at right angles and place his story and entire era as one small element of a vast science-fictional cosmology was inspired.
Incidentally, talking about the Warrior's Dawn era being set in a prehistoric/mythical Britain is way off: aside from a few moments in flashbacks, Slaine doesn't set foot in continental Europe, never mind Britain, until Dragonheist. All the early stories are set on the floor of the Atlantic, and most of the flashback stories, Slaine the King, and almost all of Horned God are set on the floor of the Irish Sea. Slaine has always been fantasy on a vastly more ambitious scale than its barbarian wanderer trappings suggested.
Still hate those bloody leyser guns though.