I waited until both parts aired before watching them, because I hate cliffhangers. I'm glad that they did this mid-season and not as an actual cliffhanger over a season break.
I thought it was pretty damned good. Both parts. In this case, unlike most Trek, the second part actually delivered and didn't feel like a cop out. Calling in the Krill was bold. But they've laid some groundwork for an uneasy alliance already, and this built upon that, so cool. Isaac came through, as most people figured he would, and of course it was "the power of love" or something like that. But it worked for me. Isaac seemed changed after his reboot, like he was ready to toe the line, but when Kaylon Primary threatened Ty, we knew he wasn't gonna let that go. But it came up in a reasonably plausible, dramatic way. So... cool.
Those who predicted Isaac wiping out the rest of the Kaylons, kudos to you! Not all of them, and it was done using some technobabble (EMP over the comms? Really?) But whatever, he sacrificed himself to disable the others and save the ship, and that's good because he's gonna need a few points on his side to build back some cred on the ship. He was, after all, responsible for the deaths of several Orville crew members and the entire attack on Earth and everyone who died in it.
No, it didn't really make sense that the Kaylons needed another planet, since they obviously have huge amount of empty space on their current planet. And it made even less sense that they'd travel all the way to Earth just to kill all humans. If they wanted another planet, I'm sure there are plenty closer to their homeworld, including some far better suited to them. But whatever, I guess we needed to have "the whole human race" threatened, and this is how they did it.
Some things you let slip, as long as other things work. Whether or not an episode, or a show in general, works for you, depends on which things are important and which things you're willing to let slip. The premise of them attacking Earth didn't make sense, but after all the other pretty good drama up to then, and the damned good CGI battle scenes, I could let it go.
Overall, I'd say this was the high point of the series thus far, or at least one of the high points.