Despite it's well known flaws and frustrations, Metal Gear Solid V: Phantom Pain is still a masterpiece of a video game. The concluding chapter in the franchise looks and play beautifully, with a freedom not allowed in any previous MGS title.
The definitive edition also includes the prologue chapter Ground Zeroes, which is well worth playing before jumping into Phantom Pain as it sets up some of the stories complex strands (benefiting seasoned players and series newcomers alike).
If you haven't played any of the MGS series previously, I would however recommend starting earlier in the chronology, especially if you're keen to dive into the deep lore of the games. If so, before starting V I'd recommend playing MGS 1,2,3 and 4 (obviously) but also MGS: Peace Walker as chronologically in the series this is the prequel to V.