Kuro has the spoilers. In short - GAINAX managed to end the anime off the running manga; certainly it's no Mahoraba, but I guess nothing is. Another gold star on the resume of Seiji Mizushima, who I mostly know as the director of Dai-Guard.

(In respect to some comments, GAINAX buried the ghost of GAINAX Ending with Gurren-Lagann, so Hanamaru is only significant as a workaround for the original source.)

UPDATE: Yumeka says:

Hiiragi, however, was probably the most unique character – she’s knowledgeable beyond her years without being snobby nor stoic, and yet her intelligence doesn’t interfere with her image as a cute little kindergartner.

I think the moment where Hiragii forgot that her classmates are illiterates was very natural and fitting.