If it wasn't that i really loved this series from the very beginning, despite all the incoherences and what not, i would have disliked this. I started watching animes just last year, and this was one of the very first titles i came across. I never read the novel, but just sticked to the anime adaption, because at the time i cared only for animes. After having watched the 3 seasons i didn't feel like reading the last volumes, so i just waited for the 4th season. I felt like many things were rushed, but i was still able to accept them.
I'm in a state where i like this series so much that i am able to forgive all the bullshit they threw in there, just smiling at them and wondering "what if".
But getting on an objective point of view, seriously:
Spoiler for much spoilers:
1) When Saito is first summoned, doesn't he give a flying crap about what his parents may think? And when he gets back, how is he meant to explain everything?
2) How the fuck does he get the plane? Rofl, that part me laugh hard: if i ever tried to get in a military base i'd probably get shot on sight, but he's Zero familiar, and he's acknowledge by Japan's government aswell, so they let him do whatever the fuck he wants, let alone ride one of those F16, right.
3) Just how much convenient was that that exact day there was an eclipse in his world? And how was he so sure that it'd have worked?
4) Did they turn Derf into a plane, or into runes just not to make spectators sad or what? Kinda rapes the "sad" moment where Derf "dies".
4.5) To launch the last explosion, Louise drained all the power of Saito, but it didn't result in any kind of loss for the latter: convenient or is it explained in the novel?
5) Did i have to wait for the last episode to have Saito dressed in a different set of clothes or what? Did he use that shit for years, or Henrietta opened an industry to reproduce his clothes nonstop (since louise destroyed them every episode)?
6) They involved Tiffa and made her the 3rd or 4th (whatever) Void user, but she didn't really play any important role: she was only able to use that only spell and to slam her boobs around. Also, if anyone had time, care to explain how can Saito be the familiar of 2 mages, what does this cause, and many more questions that could be born from this? Is it explained in the novel?
7) I wonder what could people think of a wacko dressed in mage clothes hanging around in Tokyo, eating stuff. Care to change your clothes into something more... appropriate, miss Valliere?
8) Those 4 mercenaries... did they have some more space in the novel, or they were just side characters fated to fade away after one episode or two?
9) The whole desert elves thingie... was it more developed in the novel, or is it just me that felt that this thing was rushed? There are still many questions left pending about this...
The second half of the last season felt rushed like hell, many characters faded away just after one episode, and i could list an infinite amount of incoherences and what not... Despite that, i still loved this series.