@Klashikari, you say there's lack of characterization. I never thought so, and I almost instantly liked Sousuke, and Kaname too, even if less than him. Ofc, everyone's entitled to their opinion and feelings about a certain thing, here's what I think:
It's been a while since I last watched the series, and even though I watched it many times over, I don't quite remember all of it. But from what I remember, at least in the first 7 episodes, there's plenty of "characterization", especially regarding Sousuke and Kaname.
First episodes show us the "Fumoffu-Sousuke", always military-oriented and unable to adapt or even understand normal high-school life. He's always suspicious of what happens around him, follows Kaname closely and gives her those stupidly-amusing reasons for being there when she sees him.
Kaname is the authoritarian and no-nonsense girl we all got to know so well, organizing things in their classroom and smacking Sousuke every time it's required, while also showing signs of starting to care for him in a romantic way.
We also get a peek at what kind of man Gauron is when he shoots that Russian (?) officer on the bridge.
We also get to see Kurz as the ... well... the Kurz that he is
, and Mao as the one who has to suffer both of him and Sousuke
And then comes the plane hijacking. We see Kaname scared at first and then angered about the tests that are being done on her, surprised and confused when Sousuke rescues her and tells her about Mithril. Then we see her confident and optimistic on the hills near the airport, encouraging Sousuke when he thought there was no way out, and angry when he suggests that she should escape alone while he and Kurz hold up the enemy.
We see Sousuke struggling between obeying the orders given to him, and his desire to save Kaname, thinking of what happened to Sarah Miller (imo that last part of ep. 4 is one of the best parts of the series), then deciding to tell Kaname the truth about him and Mithril, being a pragmatic and self-sacrificing person / soldier in the hills, ready to stay behind to give Kaname a chance to escape. We also get a little info about him and Kalinin's common past.
There is probably more in those episodes (Tessa, Kalinin) but I think I've written enough.
As for the Behemoth and Danaan hijacking arcs, I don't recall them very well, but I'm pretty sure there's enough characterization there too.
I DO have to agree with you on Sousuke's LD-struggle, I never understood where or why it started from the anime. I just assumed it was a lack of trust/concentration on Sousuke's part after what happened to Mao. Not quite a minor plothole in the story, but not one that would ruin it either, imo.