SO ready for science!

This is purely opinion, but I think his beard should be more grandiose and beautiful. Just flowing down right past his tie! Oh, also, the hands look maybe a bit flat on the newest version, I actually thought they had a little more depth in the original version. Maybe experiment with shading them a little more to get that effect again? Otherwise, looks like a pretty snazzy scientist!

I definitely should round out his hands a bit more when I get home. I wanted them to have the basic shape of hands for carrying things later.

I have been working on his sides(platformer-type sprites) and I just can't get the perspective right...

You might want to try interlaced dithering.

I can't help but notice that is all the same picture, and none of it is pixel art.

maybe try putting shadows at the bottom of the headphones so the read as round.  I would make sure to have a portrait of the character in the menu or dialogue, in which it is obvious they are headphones.  Because they are recognizable as headphones, but I think only after you tell us that they are, infact, headphones.

This!

I thought maybe for his idle you could have him put it on and chill out to emphasize that they are headphones.

On all of your views, it might help if you had the ear parts obscure his face slightly and moved closer together, so they don't look attached to his shoulder blades, and have a more realistic perspective.

Additionally, if you could change the color the the headband, so it might not clash so much with the side and back views of the character, which are oddly devoid of detail, not to mention the green shirt design on the front.