Alright, that looks great, I just have minor comments.
One would be about the head spacing. I think it should overlap a bit more as he sits down, so it finishes a nice arc as opposed to having such a linear path. It feels like the chin hit a table top or something. Here's what I mean:
Watch out for his left arm, it feels a bit IK until x46; especially around x29 and on, where his elbow goes in but the rotation of the wrist is the same. And watch out for x40 to 43, it feels like the hand is stuck in space as the rest moves. Overall it looks like it's on the same horizontal path. When he turns around, in the x25 area, his body could be rotated sideways a bit, which would give the arm a little path in the path, so you get an arc.
I like the arm action when he sits, but I'm inclined to say that it is a bit fast. I would at slow down the arm pull back, which feels literally like he's pulling his arms back, instead of them naturally bouncing back. It's okay he that is his voluntary action, to pull his arms back, but in this shot right now, it looks like he's hurrying to pull them back, which feels a bit weird.
Contrasted with this fast movement are his feet, which feel slow. Those I would speed up by at least 30%, so it doesn't look like he's deliberately keeping them off the ground.
Almost there, just little things. It's overall really cool though already!