If they would put just slightly less effort into it the film would've just been 80 minutes of black screen.
Sorry for being negative. The film consists solely of cliches and themes used a thousand times by now in horror cinema. If you have seen any other horror film besides this one, you can predict not only the ending but almost every scene and every line of dialogue. Every hint, every supposed twist we have already seen before.
The story is just slapped together and the film expects you to buy a lot of things. Nobody really bothered with acting either. The composite shot of an elderly man scaling the wall upside down was hilariously cheesy.
The ending was ok, but since 90% of the film felt like waiting in an elevator, it doesn't matter much. The creature make-up was surprisingly good, so I don't think it was made specifically for this film, seems too costly to such a minimal budget whatever-type of film.
This feels like it was made by someone who has never seen a horror film, but checking the director's bio proved me wrong. So, I guess there were other reasons. Maybe Jason Blum just said, "Come on, I got this script I found in the attic from 1995, let's slap something together in a week and make some easy cash".
If you're planning to see this one, and you have seen horror films before, watch the first 10 minutes and you will build every other scene and the ending in your head.