I think it took the brickbats it got because
1) Shinbo fans remembered Tsukuyomi Moon Phase and what a win that was .... and whereas PPD was random gold, inserting that on top of Negima!? had mixed results. It also seriously didn't look like Shinbo was really paying attention to the show (has the paycheck cleared yet?)... even the original plotline had an "I don't care" vibe for some viewers. Even the Shinbo fans wandered off by ep 20.... I watched the raws to completion but only out of some morbid sense of duty.
2) Negima manga fans ..... want to see the manga storyline adapted. How hard is that for the anime staff to understand? If you're going to do a Moby Dick adaptation, fans will not appreciate you giving Moby laser deathbeam eyes or Ahab having the hots for his first mate
I was fence-straddling for the first 2/3 of the series --- I loved what Shinbo had shown he could do in other series, I loved the manga storyline, I loved the SHAFT art stylization of the characters, I loved that a lot of tier 2 characters got a fair amount of screen time, etc.... As the anime-original part of the storyline progressed, my interest waned.
I got about 10 episodes of good stuff for me... and the rest was just "I didn't care about the story or the characters anymore and it really wasn't funny to me".
Despite that.... I really think a fansub group should finish what it starts or hand-over the material to another group who will finish it. Mahora ... their whole website is "all about the Negima" and they appear to have stalled completely.... yet seem to have steam to pick up other shows.
At that point, rather than criticize -- I'll point to the Yamato Nadesico Shichi Henge fansubbers who carry on to the end despite the utter trainwreck the series became
Kudos to them.
Back to reading the Negima manga .... ... ...