I have sunk about 15 hours into the game so far, and I am still having a blast playing it.
There are several different ways to go about your missions, and even after a dozen hours of playing Im still finding new paths through the compound, or different points of entry. It may be just one map, but there are a lot of nooks and crannies to explore. Couple that with a ranking system and ocd gamers may find themselves doing multiple run-throughs just to get the S rankings and all the collectibles.
If youre not into the side content though you may not get as much play time. It really depends on you. It is a little on the short side. Just a few more missions would have been very welcome. But I have really enjoyed the time Ive spent with the game and Im looking forward to Phantom Pain.