I'll give it a 5. There's a much better episode hidden in this one, and I think that's the one people are giving high marks. But it's ruined by slow story telling and logical leaps.
1: There was no need to suddenly require Discovery to be used as a lab for an incredibly dangerous experiment WHILE rescuing refugees. If the writers wanted to make that be a thing they needed a cause. None was demonstrated.
2: Murderer Prisoner Guy now takes that award for Boring-Ass Speech That Makes You Reach For The Remote away from Archer and his Gazelle Birth. At least Archer had the decency not to tell that one while a black-hole-thing was about to pop intp view minutes and kill everyone. There were other moments just like it that absolutely killed the action. Even Beyer can write better than that.
3: Burnham is now speaking softer and softer every episode. By the end of the season she will be whispering into a straw which is submerged into a milkshake. I get it, actors in general are on a single minded crusade to pass Matthew McConaughey on the road to perfect incomprehensibility. The less you are understood the more dramatic you are. Am I starting to long for the Burnham Sermons?
4: Risa. It's nice that Risa somehow remained a vacation planet.. through The Burn. WTF
5: Parasitic-Beings? Uh, please tell me they didn't scrape the barrel for one of the worst bad guys in Trek lore.
good stuff:
1: Reno
2: Culber
3: Kovich
4: That Vulcan ship
5: Thought they were going to kill Reese. Glad they didn't.
6: Season 4 is reminding me that I miss Lorca. He would have just shrugged and left Murderer Prison Guy before we had to hear his sad sack autobiography, and he wouldn't have bothered piping it in to the bridge, later.
7: Interesting to know the Iconians are still around.
This might have been the worst episode of Discovery, yet, IMO. They have no sense of urgency, no timing, and feel the need to keep multiple concurring plots going when sometimes it's okay to focus.