It is difficult to assign a proper rating to a show as unbalanced as this one. This uneveness isn't even a case of certain elements of the series being handled better than others; Kurenai is both pleasing and disappointing in every one of its aspects. The animation is distinct but marred by noticeable low-quality moments, the characters are as engraging as they are entertaining, and the plot moves from being confusing to entertaining to downright stupid. There are no triumphant highs or deep, dank lows in Kurenai, but this anime does enough seesawing between entertainment and disappointment to lead to a mediocre viewing experience overall.
Kurenai does do some things right. This show's biggest strength is its complex setting, which the viewer is thrust directly into from the very first episode. The characters and their actions make little sense at first, but each of their personalities and histories is revealed as the series progresses, leaving the viewer with a very thorough understanding of the situation by the time of the climax. Another one of Kurenai's most enjoyable aspects is the relationship between Shinkurou and Murasaki. The boy-suddenly-acquires-loli plot device has been used in other works, but it's handled well here. The most enjoyable moments of this show and found in the midsection of the story, where Shinkurou is simply trying to get through daily life while putting up with Murasaki's eccentric behavior.
It's a shame that the staff had to throw in some hamfisted attempts at action and heavy drama into the mix as well, because Kurenai does well enough up until these scenes are introduced. It's not that these moments don't belong in the show, because they are most-likely included in the light novel source material as well, but they are handled so poorly that I almost wish they were left out. During these scenes, whatever was interesting about Shinkurou is brushed aside to make way for a bland "I'll protect you" male lead, and towards the end of the show, none of the characters behave consistently. The series finale is especially insulting because it absolutely trashes the intricate plot that was being weaved up until that point with a complete cop-out of an ending. It just might be better to stop watching this two-thirds of the way through.
I wouldn't say that I wasted six hours of my life watching Kurenai, but I wouldn't suggest that you set aside your valuable time for this.