It's a good game.
Well if you disagree I suppose I should say that you're entitled to your opinion and that we can all get along amiably despite our differences. But I'm not that kind of guy so, let's restart.
Meanwhile Eternity's Child gives you control over your character's generous air time, brilliant bullet mechanics and one way platforms. This is reflected in its level design as you fall through gaps in spinning blades, beat otherwise unstoppable swarms with clever charged shots and navigate your way around increasingly cleverly positioned platforms that can only be jumped and shot through one way.
Finally, I think the major key to the replayability of Eternity's Child as well as Mario Bros. and Fancy Pants is their predictability. They didn't need to try and startle you with clever plot twists or jump-scares because the games had the balls to tell you, "this next bit is brilliant, go on, take a look."
In short, what made these games awesome the first time is the same stuff that makes them awesome the second, third, fourth, fifth and however many other times.