Yea its a shooter but its so much more and I think it rather stands out in the overly saturated FPS market.
It's set in a fictitious old west and you take control of John Marston, an outlaw who is just trying to settle down with his family. Just like with Fallout you can make any number of choices to be a "good" guy or really spread the mud and get your hands dirty.
There is a lot of optional content in this game but you can opt to just play the main story for a quick game. However I think most of the extra content is implemented really well and worth exploring. If you are not the best shot in the world, like myself, there is an ability to slow down time and mark your targets which can be really helpful especially if you are being swarmed.
It's a great game with a large open world with an ample supply of weapons where you can do as much or as little as you want. Here is one of the many trailers.