Developer Two Tribes isn't letting this delay get swept under the rug however, as it chose to admirably take on the exact reasons for the missed deadline in a full, honest blog post.
Apparently, the level design just wasn't where it needed to be, so they ditched the structure and decided to go with a more open approach. A number of other facets of the game were also perfected, like performance and graphical output.
The entire endeavor is summed up perfectly by this quote from Two Tribes co-founder Collin van Ginkel: "my ego isn’t big enough to think I’d do a perfect job without the need for some serious testing." Kudos, Two Tribes.
I've always said that it's a great idea to keep people updated with the progress of your game, regardless of the situation. This is especially true with some Kickstarters, where developers will often will refuse to update their progress even months after obtaining their goal.