Most people say its a "preview" of the Phantom Pain gameplay, storywise it is the prologue to TPP...
That said I've put 30-40 hrs into the game, even though you can beat the "main quest" fairly quickly. There's plenty of game there if you go after everything. There will be a few differences/enhancements to the gameplay here and TPP game, like the time accel and mother base system, but the sneaking game is pretty much the same as GZ.
sounds like a different type of game then TLOU...so you must be referring to the characters, story and game mechanics being better then TLOU...still not sure if TLOU vs MGS is a fair comparison but we'll see