Minor spoilers, I'll try not to give too much away.
- Episode 2, Bête Noire, the episode ends in a positive note, but is more in the weird category in terms of endings.
- Episode 3, Hotel Reverie, generally ends on a happy note however it has a lot of sad moments within the episode.
- Episode 5, Eulogy, is probably the saddest episode of the season. It's also arguably the best. The ending I think is a positive one. It's a general theme of loss and closure.
- Episode 6, USS Callister: Into Infinity, I think of you found the first USS Callister episode to end on a positive note then I would say the same applies here. They both end with a similar feeling.
It's interesting because in an interview with the creator he mentions that one of the loose goals with this season was to highlight the positives with technology.
Looking at the first episode, the technology to save the wifes brain is amazing technology! She would be dead without it. The cost is so minimal it's an easy choice.
If course we know how the episode goes, but it is funny that at face value the technology is great, it's what happens next that is the downfall.