This was another great episode. It definitely evoked "Who Watches The Watchers," which is one of my all-time favorite Trek episodes.
The opening sequence of Mercer trying to find a drinking buddy was great. It's kind of a shame that they couldn't have included Claire, Alara, and Isaac, just to close out the season with a peek at everyone in their down time. I got a kick out of the suspicious smoke in John's quarters, and appreciated the open-shirted ensign, but I wonder if that scene foreshadows a coming divide between John and Gordon, thanks to his promotion. And, of course, the game with Bortus and Klyden was hilarious.
The main plot was wonderful, and really delivered the kind of positive message that Trek used to be known for-- and both the interphasic planet and Isaac's casual volunteering to go on a 700-year diplomatic mission were great sense-of-wonder ideas. The episode really hit all the marks. The moral of the story, that religion is an unavoidable, but survivable, symptom of civilizational adolescence, was both uplifting and very timely. And the glimpse of the "future" civilization, from the alien megastructures (which I do think would have worked better in soothing blue than ominous green) to that silvery ship to the glowing white robes, was very nice.
The only real plot hole-- or rather, unaddressed point, unless I missed something-- was that this planet will continue to appear every eleven days. So what will the Planetary Union science ship encounter when it arrives? They should have thrown in some line about the aliens using their technology to prevent further crossovers.
Another thing this episode demonstrated was perfect examples of good Orville humor versus awkward Orville humor. Moclan party game: Good. Admiral still on the phone: Awkward (although I did laugh).
The relationship between Mercer and Grayson reached a good point for the season finale. It was typical of the mature writing, so rare in the media these days, that they would come to this conclusion based on a story element from the main plot. I still think they will eventually get back together and that their time apart will ultimately prove necessary to solidify their relationship. The "Menagerie" episode demonstrated that their youthful marriage probably would have imploded under any circumstances, but we've already seen them both grow a lot in one season. Hopefully that will continue.