It's rare that a sweatshirt looks truly great on anyone. Notice how the WAYWT fits with multiple visible layers tend to receive more thumbs up. The multiple layers provide visual interest since both the color and texture of your top half is no longer uniformly monotone. Likewise, even a plain v-neck s/s tee provides you with multiple colors and textures on top since your bare skin can be thought of as an additional layer.
But a long sleeve, crew neck, single color sweatshirt with few details is simply bland looking when worn by itself. It's like having 10 acres of schlubby gym fabric covering every inch of your top person. Just look at the guy above with the mustache wearing the sweatshirt! Wearing that sweatshirt together with his droopy eyes it says I'm hungover from last night, all sweaty from my recent trip to the gym, and didn't even bother to shower.
I do think the sweatshirt could look good if you paired it with a down vest though. That would add a pop of visual interest, breaking up the blandness the plain sweatshirt. But perhaps that would be warmer than what you're looking for. Otherwise I'd just avoid wearing plain sweatshirts all by themselves.
I agree with almost everything except that this photo looks bad. I think its one of the rare sweatshirt fits that looks like it fits him and is not an amorphous blob.
and max_r I like those MMM's I just wouldn't wear them with the black jeans in the first photo. I think they look great in the last two.