The premise is simple: some friends get trapped in a sauna, it keeps getting hotter, and they've got no way to escape.
The movie is surprisingly watchable for such a premise. It wasn't scary or anything, but as you get to know the characters more and more, and as their time runs out, the movie draws you in. Unfortunately, it takes far too long to get you drawn in. By the time you're fully invested in the characters and their fate, the movie is 95% done.
It's not easy to make any movie that's confined to such a small space. So that 247 did a reasonable job at it is commendable.
While 247 isn't the best movie in the world, if you've got nothing else, it's not the worst choice you could make.