I played this game on my stream (VOD).
Overall, this game was fun but made me very anxious, so I could only play so many levels in one sitting. It reminded me of Heave Ho, which is a co-op game I loved playing with my family. Somehow, this game gave me more anxiety though, I'm not sure why..
I had fun through the levels though the controls were a little hard to grasp (pun intended). I sometimes would click the wrong mouse button to launch the grappling hook or jump, but it was ok overall.. Maybe with a controller and the left/right trigger it might work better.
One suggestion I have is to have a way for the player to view the entire map. Sometimes I didn't know where the exit was or where I had to go, so I had to swing blindly and see where I ended up. If I played a level enough, I would eventually learn where things were, so why not have a map or a way to move the camera around while keeping the player still from the get-go? :) That might make the game easier for the player to plan their moves.
Another suggestion is a way to jump off walls. I had a few instances where I was grappled to a vertical wall, and I was unable to swing much, since if I hit the hall my inertia would stop, and I couldn't "bounce" off the wall. In the last stage I was at, it caused me to die since there was really nothing I could do to climb back up the corner. Maybe there was another way? but being able to swing my way up would be nice.