Following the episode "Wolves at the Door" that seemed like a generic, dress-up-as-scout-troopers, infiltrate a base and ultimately get captured type of episode, this episode strikes me as the most interesting and awe-inspiring one to come to mind.
The concept of this world between time and space does seem a bit strange for the world of Star Wars, as it is difficult to imagine utilizing this concept in a Star Wars film or portraying it as scientifically as this episode did, yet the writers managed to use it to their advantage. The concept could easily be exploited in other material in order to ret-con facts and be used as a throwaway, lazy storytelling trope to justify plot holes. However, this episode clearly dismisses this unfortunate possible path by showing Ezra (the audience) how its implications are dangerous and unpredictable, reasoning why it shouldn't and cannot be used very often. The world itself is gorgeous, with the swirling arches and cinematic blue flames portraying an artistic simplicity of such a grand concept, showing the artists' ability to handle the delicate idea of creating a universe between time and space.
Ahsoka's reintroduction was an interesting choice that inevitably payed off, as it clearly answered any questions regarding her fate, allowed her character to get caught up in present events so that she could be reintroduced physically (I hope) to the rest of the characters, and allowed for an aesthetically pleasing parallel (with Kanan's fate) shot of her holding back flames to save Ezra, possibly foreshadowing her future death as sacrifice. Speaking of which, it was pleasant to see Palpatine easily access the world and try to kill Ezra and Ahsoka then, although his physical limitation justified his loss.
The B-story was also interesting (for a change) with Sabine realizing she's trapped and might as well interpret the art to save Ezra, while the scene of the ship tilting on its side was like that of a space action movie that felt exhilarating to watch. The score used during the scene where the cave is being closed was more beautiful and memorable than any I can recall for this show, as was the final shot of Ezra and the clouds above the temple.
All in all, a very interesting, beautifully animated, necessarily told episode, the best of which I personally believe we have seen all season, let alone for the entirety of the series.