Thresh: Should not stick onto a spell shield
Just my opinion, but I don't think Thresh's hook should stick onto a spell shield.
Visually, what is this representing? His hook breaking through the spell shield, to latch onto the champion. The is not the definition of the spell shield.
Additionally, unlike Amumu--who immediately travels the his target--Thresh maintains significant power over an area for so long as his hook remains. That there's not way to diminish his power beyond dodging the hook, seems a mistake. Spell shields are already unpopular; this just feels like something they should do. I also think Thresh's hook should detach if you use a cleanse on it" like Fizz's fish detaching. It just feels unexpected, how persistent Thresh's hook is.
Most importantly: Thresh is already a really strong champion. He's always balls out tanky, he gets a really long ranged base attack, he has a bunch of CC, and, oh, attacking lowers his cooldown. If one hook gets blocked, he's got another one up in just a few seconds. He doesn't need to have this level of power.