Stormblade is... the artsy type. Or about as close to that as you can get in a Scyther, at any rate. Idealistic, emotional, curious and eccentric by his society's standards, he always sort of stands out among them, but fits in better with ourselves; he's very human, in fact probably too much so (not that a lot of the Scyther society in this universe isn't a bit too human in many ways), though unlike Razor turns out post-Rob, he is human in thought more than action.
I guess that probably makes it easier to sympathize with him than the other characters in the Scyther spin-offs, which might explain why a lot of readers seem to really like him. I don't like him as much, precisely because of this humanity; I guess I find him too sympathetic to be as interesting as Razor and Shadowdart, but that's just me. It also irritates me now that there are several bits in The Fall of a Leader that feel kind of anvilicious, almost as if the point of the story is to preach that Stormblade's opinion is right and Shadowdart's is wrong, which was not the idea. And I am absolutely terrible at attempting to write something that sounds like an emotionally healthy romance, which is probably also a large part of why I generally prefer the Shadowdart parts of TFoaL over the Stormblade ones. It says a lot that my favorite Stormblade bit is when he returns to Shadowdart after tearing that Letaligon apart.
But that is not to say I don't love Stormblade anyway. He does have issues, after all. Primarily, he's really clingy and dependent, though this sort of swings back and forth depending on his general state of mind; when he's unhappy or worried, he needs to hang himself onto somebody else that he sort of lives through and is completely incapable of being alone. ("Loner", the name Pearl gives to him, is decidedly ironic in this regard.) At first, with Shadowdart and Razor, it isn't so bad; then Razor leaves and he is unhappy so he starts to cling to Shadowdart as the only one he has left; then Shadowdart gets more distant and he finds Pearl to cling to instead; then she dies and he clings to an idealized hero image of Razor to keep himself alive; then he realizes the real Razor is imperfect and really nothing like him and returns to clinging miserably to Shadowdart as the only one remaining; then he leaves the swarm and clings to the random wild Pokémon he can find and have shallow one-minute conversations with as they try to convince him not to kill them. It would become Nightmare next, except it is kind of hard to cling to Nightmare, as she is worse off against the swarm than he is himself and therefore not much of a solid rock to stand on. Ultimately, I think his friendship with Nightmare is very healthy for him as a way to force him out of this clingy state and allow him to be more independent while remaining social, especially since while the Scyther are dueling to find a new Leader, he has pretty much taken over the role, and therefore he isn't as isolated from the rest of the swarm. Stormblade and Nightmare understand each other well, but in a mutually supportive way, not one where Stormblade just attaches himself to her as the reason for his existence.
That's not to say his relationship with Pearl was bad for him, per se; he just didn't have the emotional strength to handle it right. She even tried to tell him he needed to stop being clingy (though she only noticed it when it was Shadowdart), but ultimately, he clung to her anyway because at the same time Shadowdart was being distant and kept dueling the Leader and then he was existing almost exclusively for her.