Not bad bud.. have some suggestions.

1) As he starts to pull up i think he would arch his neck and back a bit more to compensate his weight and give him some more momentum to pull up. As it looks right now he should fall over on his face with the way his weight would pull.

2) After he stands up maybe sit him back on his hide legs a bit more to give him some more secondary motion. He's leaning forward to much in my eyes still.

Great start and great model rig job by the looks of it.
Would be fun to play with.