Great concept! I like the idea of swinging around the city spiderman or mirror's edge style while blasting mechs. Definitely had my favorite enemy designs of any of the games I've played so far. Really fun navigation mechanics too -- I wasn't good enough at it to really get up speed, but being able to whip around corners and on top of buildings could be super fun.
There were definitely a few bugs that impeded the gameplay: I kept losing my hook, after taking damage, I would sometimes get kickback even after the damage was over (and it seemed to just keep applying a physics impulse to me every few seconds). When climbing buildings, it was difficult to get over the lip of the roof. Maybe adding a kick off ability that allows you to jump away and up on the wall would make the navigation easier? I also had problems finding the heart in the medium size mechs (second wave). Maybe making the top back of them transparent so you can see the heart inside that container section would make it clearer?
The level design was great though -- I liked having a sandbox city to hop around in, and watching it slowly get destroyed by the big mechs kept the intensity up. Also, making each mech variation a bigger design was a great way of having progression. Great job, guys!