I thought it was a bit on the odd side. It started out as one sort of film and ended up as another. The ending was a bit silly.
That's because it IS two films. It was originally called The Cellar and it was part of Paramount Pictures low budget division where they made films on low budgets of $5 million or less. The movie was filmed and then shelved as they didn't think it would make any money. JJ Abrams company Bad Robot then bought the rights to it, re-wrote the ending to tie it in to the Cloverfield universe and did reshoots. It's basically a cheap cash grab to make some money from a movie that wasn't going to.