The only MG game I ever played was 5, and I first played it a few years ago and didn't enjoy it enough to continue past the second mission. I tried playing it again a few months ago in anticipation for DS and ended up finishing the game, and a portion of the post-game, and really enjoyed it. It was recent enough such that I haven't mentally put the game down yet, although I doubt I'll play again anytime soon (ever?).
I'm not the biggest fan of stealth games, but I've opened up a bit after playing MGSV.
Graphically and gameplay wise, it's awesome! The sparse story and lack of things to do killed it. It plays differently from pretty much every other game in the series (aside from Peace Walker) so if you do play any of the other games, you're in for a shock! The others had a dialogue/cutscenes/easter eggs that compelled you to see what's next, though. The narrative kept me going and, in this day and age, they probably aren't as engaging either.