It can be tricky to give characters good motivations, and making them funny can also be a bit harrowing. But for some people it comes naturally. Comedy doesn't come to me very naturally, though I did manage some comedic moments in my script where appropriate.
Motivations aren't that hard, though. Good motivations might be difficult to work out, but any motivation is better than no motivation, which is what all the characters in his script had.
I'll have to clarify that my exhaustion and attitude regarding classmates' works is that I'm in my final semester of college, I've read dozens of people's short stories and scripts, and there's very little imagination in 8 or 9 out of 10 works. If I had a dollar for every story that involved alcohol, bars, clubs, parties, relationships, or angels/demons, I could buy a nice dinner for two. Yeah, I don't get the angels/demons thing either. I think it comes from people being inspired by Supernatural or generic young adult novels.
Last semester, the screenrwiting class I took had this one girl whose script was about a serial killer who had a devil on his shoulder (named Asmodeus; oddly, another girl completely independently also had a devil named Asmodeus in her script). This devil compelled him to kill young women to keep him out of hell. As someone who's also taken several theology classes, this kind of thing drives me nuts. What's worse, the story was basically that he manages to kidnap her, brutally torture and kill her (in graphic detail), and then... that's it. No meaning, no greater message about humanity, just terrible premise with an awful execution (pun intended). Which is funny, because stories without any meaning or message was exactly what my professor told us was bad in the beginning of the class, but that somehow slipped this girl's mind. You could tell my professor was trying to be kind and constructive to her script, despite previously talking mad **** about a horror movie he saw that had the same exact problem.
What made the situation even worse was that this girl would also be the first to chime in with criticisms on other people's scripts when it was their days. I don't think a compliment ever came out of her mouth. She'd tell people that she thought their characters were flat and stuff, despite her script being no less flat than theirs. There was one day in particular where there was one minute of class yet and we were wrapping up, but she raised her hand right before the professor dismissed us just to criticize the other student's work, and then she immediately packed her things and left. I'm just thankful she wasn't there the day my script was workshopped, because by then I was pretty fed up with her.
My creative writing classes were generally better. But the last two that I took were ones that you had to apply to get into, and only 15 people would be accepted, so it filtered out a lot of the people who wouldn't have been good contributors to the class. There were still some irksome scripts there, but everyone there were nice people and more serious about the literary craft in general, so I have a lot of respect for them. Problem is, I was writing silly alien sci-fi stories set in a series, while they were all tackling more self-contained genre fiction, which made me feel like a bit of a black sheep.
In this series writing class, at least, the first script we workshopped was for a sci-fi action series, just like mine. And a handful of students' scripts are for animated works, too. So I feel more at home in this class than I have in any other class I've taken, even if I scratch my head at some of their writing.
Noice or a 
Noice?