looking much better! Nice!
Alright, let's start with the root:
from x1 to x28 you might want to give it a bit more life, it's a tad floaty. Then around x28 it seems to pop back screen left and stick there till x32. After that it moves in a very straight line screen right until x40 and suddenly stops.
Always remember that pretty much all movement is following an arc (even if the arc is tiny). So if you do a weight shift over a leg, it will push the pelvis up over it as you do it. And overall, you don't want a straight line in CG land, it looks too robotic.
Anyway. The sit down is cool, but needs a bit more love. I like how slow and labored it is and how sudden his stop is (he doesn't look fat, it's not like his big butt would serve as cushioning - it's more like bone on wooden chair). So now you need to add a bit more polish to it. Start slow with the descent but speed it up as it gets to the chair (because of gravity and his muscles weakening over time). The impact would need one or two frames softening. So keep that key on linear, break the tangent, but add 2 frames of him going down in Y so it doesn't look like he's hitting a wall. When he actually hits the chair, add some overlap to the head, so you can feel the impact. You don't want the head to be all stiff.
When he leans forward from x100 to x124 his hip is not moving, make sure that you don't let it die. In an older version you had him lift his shoulders a bit as his arms move forward, which was nice, put that back in there.
Now the upper body.
After x24 to x33 he leans forward very quickly and then stops. I would slow that down a bit and keep it alive as he grabs the armrest. The other reason why it feels fast is because there's so much mass moving. You're moving the head and the upper body as one unit. You need to break it up. The head can drag or lead, rotate around, etc. as the body moves.
Since your timing of the root will change, it will affect the legs, but either way, make sure that you don't overextend them, like on x38. You don't want legs pop in and out of hyper-extension. Besides the pop you'll also get the feet to move up, because of the sticky IK. The screen left foot adjustment on x51 feels odd. I wouldn't treat it as a step, it's more of a shuffle or foot adjustment. So point the toes down instead of up (makes it look too exaggerated otherwise). Keep the foot alive as he sits down. Looking at the screen left leg from x62 to 75, it really bends over, yet the foot is stuck to the floor, which yells IK.
Always think about how each part of the body affects the surrounding parts.
Speaking of IK. The hand that grabs the armrest (make sure you don't overextend the arm around x44) is super locked from x54 to around x77, which is ok because it's holding the armrest firmly, but what kills it is the elbow. I would steady the elbow movement with the polevector, but always tie it in with the body movement, so it doesn't feel to separated.
The screen left arm is going through the chair geometry around x80.
Fix the wrist and fingers around x79, they seem to go through the arm geometry. The hand moves away for the chair from around x80 to x92, where the screen left translation suddenly stops. Keep the arc going, don't make it look like the hand hits a wall.
The other hand needs a nice pose, he looks like he's holding a wine glass like a beer mug. :)
So do another pass with those fixes and then we go from there.