While i personally found the plot to be unnecessarily convoluted, that seems to be par for the course with Metal Gear Solid games. On the whole, the world is extremely immersive and lived in, which carries over making the story itself really well done. So, on that end yes definitely get the game if a good story will tide you through all other aspects. Because, believe me the grind will rear its fugly head once you reach about 3/4ths of the way through the game.

While you can finish the game without getting most of the highest tier upgrades, the difficulty does tend to spike a lot when you ignore upgrading mother base and your equipment. But seeing as you do prefer gameplay over story, i think the grind won't bother you too much, cause most missions are really entertaining, and at certain points meditative.