So Nelacar was asked to leave the college due to some experiments that failed, but he still likes having his old colleagues nearby to help him with research from time to time, we know that much.

However, what I'm wondering is what the members of the college think of him? Do they like him? Do they respect him? Do they wish he was still at the college?

I don't think any member of the college even mentions him.

IF you talk to them during Azura's quest they will mention him, do not remember what they said though.

I don't think NPC's from the COW have the power of thought or are capable of considering anything as they're pre-programmed to do specific things.

I imagine he may have dome some experiments that the College did not condone, but he obviously isn't so morally bankrupt that he'd go full Blackrobe.

I think if you ask them about "an elf who studies the stars," they will direct you to him, but I don't remember them expounding on their opinions him.

I would presume they are indifferent to his existence these days,... I base my presumption on the attitude I have observed since my first days there. (not caring for much but the necessary obligations to society). I honestly don't care what he does... I don't hate him, but if he died tomorrow I most likely would not attend the funeral service...

"Full blackrobe" -I like that.

This is another blunder in unfinished world design, where a character or conflict is introduced, yet Bethesda did not follow up on the depth.

This reminds me of the experiments that Falion and Phinis were up to in Morthal.

Or the 4 apprentices that became "lost" that were supposed to be a part of Phinis' college quest. Seems he is the only one that doesn't have one.