Most if not all action movies defy logic and at times laws of physics. And this one is no different; it mostly defies logic and on a few occasions physics as well. 6 underground is packed with action with weak writing. Some of the dialogues were pretty annoying. For example there is a lot of emphasis on the fact that they (the main characters) are "dead" and quite a few dialogues are written to convey that message. It seemed as if the writer was trying too hard to come up with something brilliant but instead wrote some repetitive and annoying dialogues. There's a little bit of over-acting by a few characters, some cliched dialogues and somewhat predictable story. The few positives of the movie are its cinematography and sound effects. So to sum it up, it's a one time watch and even if you don't watch it, no worries there's nothing here that you haven't seen before. Just keep your expectations low and you probably won't be disappointed.