What initially drew me to Touka Gettan was Carnelian's beautiful character designs, and I was definitely not disappointed on that front. If nothing else, Touka Gettan is very pleasant to look at.
The bottom line is that this anime is not everyone's cuppa. Touka Gettan is undeniably unique, but it's up to the individual whether that's a good or bad thing. I believe this series will most appeal to someone tired of cookie cutter anime, someone who's looking for something different.
In case you are not yet aware, Touka Gettan aired (mostly) in reverse chronological order. Now, while this is not a new concept, it is a rarely used device. As a disclaimer, I watched Touka Gettan in chronological order (episodes 26, 24-1, 25) because of the way my mind works, but despite this I can absolutely see the genius of the proper order.
Touka Gettan was not made and then randomly aired backwards. The order of the episodes plays on the world of Touka Gettan's concepts of time, complementing its lack of linearity. As I was watching, I considered how each scene would have been different and how the impact would have changed if I had been watching the series in reverse order, and I could see how clever it was. The beginning of the series is the end, and the end is the beginning.
So, I can't say that watching it one way is better than the other. Both ways have their positives and negatives.
Among Touka Gettan's unique characteristics is its atmosphere. I would describe it as the strangest combination of gag humor and and morbid seriousness. I'm still not sure how they got that formula to work so well.
It's hilarious in many place, adorable in others, and downright disturbing from time to time. A lot of the elements aren't things I'm normally a fan of, but somehow it all just worked.
A handful of episodes are presented in especially unique ways, and I found this an interesting way to break of the monotony of a traditional linear presentation.
Touka Gettan is not something you can casually watch; there's so much happening, so much depth. I felt like I should have been taking notes in order to keep up. The cast is moderately large, and just keeping track of who everyone was could be difficult at times.
While I was watching, I felt a number of the characters served no purpose, but after I had finished the series I discovered that most of those characters were crossover characters from Carnelian's other series, such as Yami to Boushi to Hon no Tabibito. I think the inclusion of these characters is a questionable choice as it only benefits a viewer if they're familiar with the other series, and they truly stick out in a negative way in this character-driven anime.
The relationships between all the characters are very complex, and are more or less left shrouded in mystery (I'm not sure how much of this is because they're explained in the corresponding visual novels).
So, in conclusion, many things about Touka Gettan are frustrating, but it's arguable whether those things are good or bad. You also don't get the answers to all your questions by the end, which is one of my personal pet peeves. What I enjoyed most about Touka Gettan is its uniqueness.
Overall, I think it's an anime worth watching, but you have to go in being prepared to pay attention.
Be warned that this anime contains: ecchi, homosexuality, gag humor