It just didn't shape up to a game I wanted to buy and that really is all.
What did you expect Overgrowth would be, and how is it disappointing you?
Honest question. There's still not enough concrete about the game for me to form a final opinion (or even a semi-solid one) on it, but I do like to reserve judgement on these sorts of things... this shouldn't come as a surprise, given present company being the Dwarf Fortress forum and all that.
Addendum: Maybe you got on the Minecraft boat early enough to remember when it was just creative mode with 3 block types, no food or damage mechanics, and no mobs but a bunch of flailing Steves. I would have been a fool to have judged Minecraft based on that Alpha. Take a step back, and consider that this is where Overgrowth is right now in its development; all we see are its fundamental mechanics. It's like booting up NES Mario for the first time, pressing the forward and jump keys, watching what happens, turning it off, and then deciding whether it was a good game or not.
We've seen none of the higher-level gameplay, and nothing of the locations but raw art assets. Most of all, we know nothing of the story but snippets from the comic; even so, they've hinted at a sort of far east Science-Fantasy setup where organic metals grow and are mined, and various castes of animaldudes vie for political and military dominance. There is a lot of interesting potential for such a world, and I'm really curious to see how far they take the Sci-Fi aspect.