I am not displeased with D&D Mark V, but now that I have the three core books for the system, I doubt that I will buy any more.
When D&D Mk.III came around, in an excess of enthusiasm, I bought ludicrous amounts of splatbooks and trapbooks and monsterbooks and what-not. I feel no urge at all to do the same this time around.
No urge, and no need. I find that converting 3e, 3.5e and Pathfinder monsters on the fly is pretty much a doddle, so buying dedicated 5e monster books would really be mostly pointless duplication (and expense).
I'm actually kind of tempted to just take the concepts from 5e that really appeal to me (like the Advantage/Disadvantage system, which is great) and graft them on to my increasingly divergent rewrite of the Swords & Wizardry rules. Of course, that would require some effort on my part, and besides, if I changed the system I'm using for my FRPG campaigns again, I suspect I might encounter some petulance and surliness from my long-suffering players.