Very interesting. I'm not sure I ever really finished the other epsiodes, so I won't try to theorize too much (especially since I'm not sure a clear plot can even be found). There is that pretty old Film Theory I watched, and I couldn't help but find parallels.
The animation was certainly the best yet. The new realism of the backgrounds adds to the feeling of emptiness and solitude. There did seem to be a bit of a discrepancy when Salad started crying and his eyes were shown as normal in the next shot with that version of him. I really liked the way his mindspace was clearly different from reality, as evidenced by Hubert Cumberdale appearing to be a lifeless lump of flesh in some shots and the mirror world not being a thing in some shots.
The sounds were alo quite nice, I liked the mother's voice.
As for the story I found it to be the most interesting yet. The others were very slow and harder to watch because of the rough artstyle. This had something happening constantly, an ending and a clear plotline. The mother and Hubert becoming a real boy were very interesting details. Makes me think the Mirror Brother really was Salad's brother, seeing as he's treated differently. Salad als says he was raised under the beast's sun, and it wouldn't make sense if salad both hated his mother and was on her side. Even with alternate personalities, that wouldn't work, as, again, different treatment. Hubert I saw as a representation of Salad, a sort of therapeutic ppaceholder, so Salad could raise him and feel better about his own upbringing. Right the wrongs. However, at the end of the episode, he uses him to pick up glass and Hubert stops speaking. This could be said to be related to Salad finally facing his brother and mother pputting his past behind him. That glass was from the mirror. He used the placeholder to get rid of the mirror which represented his past. Also, just as a side note, all the fragments of glass speaking separately was a really cool touch. I also liked the bits of comedy interspersed throughout. They didn't overpower the story, nor did the story overpower the essence of Salad Fingers.
Overall a great return, and probably the first Salad Fingers I completely enjoyed. I'm really glad to see you come back at the same time NG is getting better and better.