That was... disappointing.
First of all, 41 minutes is an inexcusably short run time for a streaming-only show, and this particular episode could've clearly used some more room to breathe.
The opening space battle was nice — some well-framed action, some actual clear starship shots — although it seemed to take a peculiarly long time for that second torpedo to hit the Gagarin. But it was all downhill from there.
I had been looking forward to seeing a planetside story, after all the time the show has spent aboard ship, but the whole setup seemed very contrived (as did all the expository dialogue used to explain it). Is Starfleet's best shot at penetrating the Klingon cloaks really some technobabble "electromagnetic sonar" McGuffin from a previously unexplored planet? C'mon, seriously. As for incorporeal beings "at one" with their planet, they fall squarely into the "seen it before" category. And why (and how?) would those incorporeal beings have built a convenient wigwam perfectly sized for humanoids they've never met before?
The Klingon scenes were once again a chore to watch, thanks to the laborious marble-mouthed Klingonese (and the still-unsatisfying makeup and costumes), but more than that, they seem to have confused ambiguity with suspense. Why would Kol give someone he didn't trust free reign with his prize hostage? We don't know. Was L'Rell really trying to defect with Cornwell? We don't know. Did she actually kill Cornwell? We don't know. Why was there a room full of corpses on Kol's ship? We don't know. If she knew about that room enough to drag Cornwell there, why was L'Rell surprised at its contents? We don't know. Why didn't L'Rell just follow through on her plan and defect in her own ship, once she knew the Federation wouldn't kill her? We don't know. Why did Kol go through with the pointless loyalty ceremony if he was just planning to reveal that he knew L'Rell was betraying him? We don't know. How did he know L'Rell was betraying him? We don't know. All of these things could and should have been answered, and it would have made the episode far better. All that's really clear after all the tedium is that L'Rell wants to get aboard the Discovery for some reason, but if we had some coherent idea of her plan, of who she's trying to play and how, there'd be a lot more suspense involved in seeing how she pulls it off. The (brief) scenes in English between L'Rell and Cornwell were interesting, and if other posters are correct that more of these got edited out, that's a damn shame.
Back on the planet, Tyler and Burnham continue to have zero romantic chemistry. Saru's conversion seemed unconvincingly sudden. Even if we accept his complete change in motivations, his actual plan makes no sense — why lie to his shipmates and try to trap them there with him? Why not just say he wants to stay, and then make himself scarce? Why get violent with them, if he was actually feeling so peaceful? And oh yeah, how and why did the aliens teleport Tyler to just where he needed to be, a power they had not previously demonstrated, and which would've helped their friend Saru just a few minutes earlier?
And, seriously, why did Tyler and Burnham (never mind Lorca) forgive Saru — the ship's first officer, remember! — for his inexcusable betrayal so quickly and easily?
Meanwhile, in the background, we have the Stamets plot still going nowhere. His demeanor and behavior were interesting last week, but this week, frankly, they weren't. His character seems to have regressed, and, well, that's about all we know, because we really only got those two all-too-brief scenes with Tilly.
When other "prestige" shows (say Game of Thrones, for instance, or House of Cards) do scenes that are all dialogue between characters, with no immediate plot outcomes, setting up things to be revealed later, it's at least possible to discern what the characters are thinking about and trying to accomplish. That's where the drama and suspense come from. Here, that's missing, and a lot of these scenes just seem like marking time. If it were in service of a plot that was tight and compelling in its own right, that might be excusable — but this episode didn't have that either. Literally nothing of consequence happened, and it all ended in midair on a tepid cliffhanger with uncertain stakes.
Overall, sad to say, by my lights this was the worst since the two-part season opener.