Munchlax is definitely going to be one of the more controversial drops this month. He was almost unanimously regarded as one of the
worst Pokemon in his former tier, and for quite a few reasons. Despite Munchlax's absurd special bulk with Eviolite, its Defense was pitiable, it didn't have reliable recovery, it couldn't provide residual damage, and it lacked any form of real team support apart from phazing: a talent that proved nearly feckless in a tier FULL of right-off-the-bat physical hard hitters such as Entei, Escavalier, and Poliwrath. It seems as though Munchlax was built for thwarting Special Sweepers via phazing, but was instead placed in a tier where Physical threats could easily pick Munchlax off and where special attackers could easily wear it down due to its lack of reliable recovery.
With this in mind, one could easily say that Munchlax will do even worse in NU. One of the most ubiquitous and dangerous physical Pokemon in the tier is the Fighting-type Sawk, followed by Zangoose, Braviary, Kangaskhan, Gurdurr, and Sawsbuck, all of which commonly carry super-effective Fighting-type moves with which to nail Munchlax. However, set-up Special Sweepers (and even Special Sweepers in general) are perhaps even more popular than the latter. Munchlax is a complete stop to massive threats such as Musharna, Ludicolo, Special Samurott, Scarf Gardevoir, Gorebyss, and Exeggutor through its gigantic special bulk and ability to phaze. Because of this alone, Munchlax will be much more popular in NU than it was in RU. However, its lack of recovery, inability to cause residual damage, and bad Defense still hurts it a lot.
In conclusion, Munchlax definitely has a niche in the current metagame but it dies to a lot of common physical threats, which makes it less notable overall. I'll probably try out Munchlax on a Stall team, as its walling ability is a huge boon to the playstyle.