TMP's villain was V'Ger.
Star Trek IV's villain was modern-day Human ignorance & short-sightedness.
The difference between them and the other more straight-forward flesh & blood villains was that it didn't require phasers to resolve their conflicts, but both posed threats to the survival of the Human race that our heroes had to deal with all the same.
But TMP being "critically appreciated?" First I've heard of that. More often, I heard it bored most people to tears.
But I think Star Trek IV resonated with a lot of non-Trekkies because its primary setting was in the current day and there was quite a bit of humor seeing our futuristic heroes being fish out of water in our time (it being a feel good movie also helped, IMO).