Ivanhobe
The Extraordinary Fan(boy)
There is actually a reason for this.
During the last HJU episode (quite interesting BTW), special guest Mark Musashi commented on how as one show nears its end, the production key members start being reasigned to the following show, sometimes leaving the previous show in the hands of "skeleton crew".
Since these are sales driven shows, Toei/Bandai sort of start to five up on a show once there are no more new toys to advertize and start focusing their resources in the next toy line. It is sad, but this is the main reason why many shows start falling apart during the final episodes.
Now, as for show that actually fall apart during their second half, i would say that there are actually very few shows that fall in that category.
I love Kiva, but i gotta say that the first 4 or 5 episodes and the last 5 or 6 are pretty weak, while the whole middle portion is quite good, though it has its ups and downs.
In the case of Faiz, the show has some quite entertaining drama, but the final 8-10 episodes push the envelope too far, to the point that it almost ruins the show.
Hibiki is an interesting case; while i truly enjoyed the first half, i wouldn´t say that the second half was bad. It was different, yes, but it was still entertaining. The final episode definetily ruins it though, not because it was a bad idea, but because the execution of it really went against the build up the show had during the second half.
As controversial as it is, i would argue that Wizard had a strong first and last quarter, it was all the middle portion that i found lacking.
Really, the only show that i would say falls apart during the second half is Kabuto, mostly because the show really does become a mess after the middle point. It still had good moments, but for the most it was pure madness, and not always in a good way.