He's pretty good - you should have played him pre-nerf, shit was insane. Right now Thresh is where it's at for me; if you're good you can do so many neat tricks. He'll probably get nerfed soon, though, he's out of control good and I'm not sure how the community has caught on yet.
Ideally, you get set up like this
blue is thresh, purple is thresh's ADC, red is enemy ADC, yellow is enemy support
pink line indicates his hook
So you throw the hook behind them - if they stand still or juke forward your adc is in range to harass hard (1 or 2 autos, depends on how quick enemy support can react) and if they run into their hook you can get into proper position while they're being dragged and toss your ADC a lantern.
Mid game gets even crazier - you can jump into your hook, I've gotten into flashing->hook->go in with it->drop ult->throw lantern to bruiser->shureil. 7/0 w/l in ranked with him atm, OPOPOPOPOP.
If jungle shows up you can do some awesome ganks with your lantern, too.