Great episode. I'd give it an "A." Good mix of comedy, drama, and impressive world-building with a nice sense of awe at their surroundings. Clearly inspired by Trek episodes such as TOS - For the World is Hollow and I Have Touched the Sky and TNG - Who Watches the Watchers among others. Fortunately it bypassed any similarity to TNG - Homeward where Picard was willing to let an entire species die just to ensure that they were not interfered with, which I'm sure they would have been grateful for after they were all dead.
On TNG there would have been a bunch of conference room soul searching and paternalistic lectures before abandoning these people to die, but I'm glad that wasn't even considered here. While the Prime Directive is a good guideline for non-interference and the right policy most of the time, what point does it serve if you're so afraid of influencing a society that you allow it to go extinct? Who are you protecting if you protect them right into non-existence based on the arrogant assumption that they're too primitive to handle or adapt to the concept of more technologically advanced cultures existing (although in this case that was just because they had forgotten their spacefaring heritage)? Zero tolerance policies that take away all logic, context, and empathy from a decision making process are useless and in many cases as disruptive or destructive as the problems they were initially created to prevent by well-meaning but shortsighted people.
I also liked the bit about leaving behind the buoy to communicate with the away team that the Orville had to leave to rescue another Union ship. Someone mentioned earlier that they liked that they were paying attention to the small details like that, and I agree.
The visuals both inside and outside the massive alien ship were spectacular and some of the best in the series so far.
It was cool seeing T-Bag from Prison Break (and TNG and VOY) again as another good villain, and refreshing to see that despite the horrible things that he did to Commander Grayson, killing or retaliating against him was never even considered an option, because the greater priority remained saving his people. It was also nice to see Liam Neeson at the end and Col. McQueen from Space: Above and Beyond, James Morrison.
Not sure how I feel about the "jar of pickles" line between the Captain and Alara possibly becoming a running gag, because it fell flat this time. I half expected there to be a meta-commentary from her about how he had already used that joke before, but it didn't happen. It was nice though to see how Alara appreciates that the captain admires her strength and skills without being intimated by them like many of her other male crewmembers and friends. Some good character building there.
I also like that the conflict between Bortas and his mate is ongoing, even though they won't verbalize it as such quite yet and will say it's about other things than the baby. I can see that possibly being revisited in greater detail later on, but as it is, it's nice to not have everything wrapped up in a neat little bow at the end of the previous episode.