Marvel Knights fans will recognize the central conceit here from Paul Jenkins's Sentry reboot--longlost superheroes from another era have forgotten who they were, and so has the world. The main difference between the two series, however, is that the Sentry was a modern-day creation by Paul Jenkins and Jae Lee, while the Eternals were created by the legendary Jack Kirby in the 1970's.
In the case of the Eternals, at least one person remembers them--Tony Stark--although it's not clear why he does. There's a mythology here involving three alien races, the Celestials, Deviants, and the Eternals, and something vague about the origins of life on Earth. The script, by Neil Gaiman, has its moments, while John Romita Jr.'s art is as visually stunning as always. Unfortunately, it's pretty clear that the mandate here is to re-introduce the characters into the Marvel Universe--and not to tell a complete story. While Gaiman doesn't stay entirely faithful to Kirby's Eternals mythology, one ends up wondering if Kirby's original creation, that lasted only 19 issues, was strong enough to warrant bringing back.