Tom Ewing fills everyone who wants to know the answer to that question in, at Pitchfork*:
Thrills were what 2000AD traded in. It even calls individual stories “thrills” and its stated goal is the delivery to its readers of “thrill-power.” Every British comic started in the 1970s and 80s had its own jargon, designed to make the kids buying it feel part of a club. 2000AD was no exception: It had this notion of thrill-power, and it had a supposedly alien editor, Tharg the Mighty, a guy in a green rubber mask with a telephone dial stuck to it. Tharg really came into his own later in the comic’s history, but the credo of thrill-power was there from the beginning. The voice inherited by Millar is in full song in the first few years of 2000AD– crude, overdriven, hilarious, and fantastically exciting.
Oh, and there’s this decription of a cover of the mag. Which I want right damn now:
One legendary 1978 cover catches the tone perfectly– illustrating the story “FLESH II”, about time-travelling dinosaur farmers. The cover is dominated by one enormous speech bubble: “NO! Please let me drown BEFORE the GIANT SCORPIONS get to me!” It’s crudely drawn, but the picture– people in water; scorpion (giant)– isn’t the point. The idea isn’t to pique the reader’s curiosity, or suggest a tricky situation which a hero will have to escape from. It certainly isn’t to spark empathy (hmm…if I was in that situation, would I rather the drowning… or the scorpions?) No, the cover is pure rampaging thrill-power, designed for grins and sensation and nothing else.
*Well, filled in, almost two years ago. I found it in the comments section for Graeme McMillan’s Brave and the Bold Review at the Savage Critic. I even nicked the second quote from that thread.