I tried Storm Spirit and I don't get how are you supposed to carry with him. his skills don't seem very useful to me, at least to kill, and his damage on autoattack isn't good either, right?
He actually has a pretty damn high amount of burst damage with his Overload spell. So every spell cast gives him +90 bonus damage on his next attack because of Overload, right? This is how encounters generally go:
1. Storm Spirit lightning balls in, doing maybe ~100 damage with ball lightning coming in depending on how far he travels.
2. Storm attacks you for normal attack damage +90.
3. Storm pulls you in with Vortex, disabling you for 2.5 seconds.
4. Storm attacks you for normal attack damage +90.
5. Storm drops a Static Remnant for 260 damage.
6. Storm attacks you for normal attack damage +90 (see how Overload damage is stacking up like crazy?).
x. Storm lightning balls around to gain a charge of Overload.
y. Storm attacks you for normal attack damage +90.
He's a ganker carry because, with enough farm, he becomes this untouchable monster that can initiate from anywhere and do massive damage with Overload stacking on his autoattacks. You can't run away from him because Overload slows you and he has a disable (and he typically picks up an Orchid or Sheepstick, making his disables last even longer). And he can run away after a fight because of ball lightning traveling anywhere.
He's a difficult hero to play because you have to learn how to manage your mana properly. He's extremely mana-intensive. But he's very rewarding and very powerful.
I'll try to find some good videos of him. If you can find a video of Godz playing Storm (there are a few on joindota, I just can't find them at the moment), you'll see what a professional Storm looks like.