Given the slower pacing of Nise compared to Bake, I decided that I would wait for this arc to finish off before commenting on it again (after my last comment a few episodes back). Now that the arc is over, I do have a few comments to make.
1) Kaiki was an excellent antagonist. His scenes were consistently golden, and he gave the overall narrative some much-needed heft and purpose.
2) The dialogue in most scenes was very good, as usual. This was especially true of any scene involving Hitagi and/or Kaiki.
3) Some scenes dragged more than what was necessary, in my opinion. If Nise had trimmed some fat here, so to speak, then I think we'd have an excellent, tight, well-executed 6-episode arc. I'd only have some minor nitpicks to make then. As is, though, I'm inclined to agree with some of Reckoner's broader criticisms.
4) I honestly had no problem with the main conflict of this arc being resolved purely through a face-to-face conversation. In fact, it's kind of fitting for this series. But with that being said...
5) I get the feeling that Shinbo himself likely thought "This final episode is going to be awfully anti-climatic if we don't have a great fight scene in it, so let's make Karen vs. Koyomi seem like DBZ meets a deserted city!"
As fun as that is, it did feel a bit overdone to me. A case of trying too hard, imo.
6) As with Bake, Hitagi is the key indispensable character. As with Bake, my appreciation and rating for an episode would consistently end up higher if Hitagi had a lot of screen-time than if she had none or very little. The other female characters are good, but they generally can't carry scenes, imo (Koyomi himself can sometimes carry scenes, thankfully, but not always). Hitagi consistently carries scenes.
7) Koyomi's sisters received some decent development here, although it was a bit less than I had hoped for. The same is true of Hitagi. Tiny tidbits of new info came out on most of the characters, but not much. Ultimately, I find the overall level of character development pretty disappointing for a show as dialogue-driven as this one is. With all of this dialogue, it would be nice if more of it could be directed to characters talking about themselves in more detailed fashion, letting us learn more about them.
8) With all of the above in mind, I personally rank Bake better than Nise, but Nise is still a good anime overall.