It's been broken down at least twice in this this thread already. Playing telephone through reddit and then summarizing said game of telephone will likely lead to shortcutting of relevant details and painting a semi-accurate picture that ends up getting skewed depending on how the person relaying the information wants to spin it.
(which I am now about to do,
after linking this post, which puts together a timeline of sorts)
But basically: The Cellar was a screenplay that had nothing to do with Cloverfield. It got put into production by Bad Robot and was renamed Valencia. Early in production Bad Robot decided it should be tied into Cloverfield somehow. How that's happened, and what that did to the Valencia script along the way is still unknown, more or less.
There's been reports of people who saw a test screening saying it's not at all monster-movie-ish, but considering nobody knew at any point in the last two years that Valencia had been turned into something Cloverfield related, it's hard to say for certain whether the test-screening was actually a full version of what we're getting in two months. It seems unlikely there's going to be a lot of monster-stomping action as of now.
Basically, nobody really knows what's up, and the people who should know what's up can't really tell us shit because this film snuck up on them just as cleanly as it snuck up on us.