It plays with 1-4 player teams, yet things are set up so that a single person can still survive and do the job if they're really good. Many situations will need teamwork to get through safely, or balls of steel to get through alone. I have found only a few seemingly unwinnable situations myself, and a few of those turned out not to be unwinnable after trying. Often you will feel like you are winning against the odds, and some situations may look very easy but surprise you with how hard they can be. And when you lose, you only lose a few upgrades - all of them optional but still very useful to have, and you can try again the next round.
The maps are varied in size, but at present still mostly empty rooms and hallways with a few consoles lining them, and they do look mostly like it's a map for a game still, without furniture. That said, they are generated when you play, and this generation will almost always be fair, challenging, and giving you interesting situations. You can even have everything set randomly - if you're going in blind, you truly will not know whether you're out for a milk run or for the hardest round you've ever encountered. And if that is not your thing, you can customize the map generation extensively and use pre-set seeds to get a map you like, though at present you still can not create a custom map.
Graphics are simple, but they work. At times they will even look pretty good in the right light and right angle. Sound design is quite well done, with every sound being fitting and atmospheric. In general, the mood is one of action and shooting, heroic space marines in big armour against a tide of aliens. Until the power goes out. Standing there, watching a dark hallway as your motion tracker bleeps at you in increasingly rapid tempo while a distance counts down from 10m, stressful? Maybe. But it is the good kind of stress, and certainly a great experience.
The overall design of the game, the way it uses light and dark and how you are both easily able to shoot down the aliens at range, yet utterly helpless if they get close, is excellent. I've not seen many games that can pull it off, but SBTF manages to do so perfectly, and it manages to do it consistently.
Whether you play it with friends, or you're playing it with random people online, SBTF will provide a worthwhile experience every single round. A few quick rounds can quickly string together into hours as you try to survive the endless waves of aliens while completing your objectives, and not a minute of it will be wasted time.
If that did not convince you, a single player demo is available at