It's unreleased Steve Gerber work. That alone deserves a huge release. Gerber was a genius, years ahead of his time, and the chance to read new work from one of my favorite creators is a huge deal for me.
And, yes, Man-Thing is clearly a rip-off of Swamp Thing. Which, is an amazing feat considering he debuted 2 months earlier than Swamp Thing. And that both are based on The Heap from the 40s. LOL. I'm honestly not even 100% sure that The New 52 Swamp Thing's success has any baring on the release of this, as I remember hearing about this months ago, but who knows, maybe.
Hopefully Marvel can also find some unreleased Bill Mantlo work next.