I really like the thin-outline, pixel-y style used here. It actually matches his body shape really well so it's appropriate.
The shading on most of the body is great, with the right kinds of crease lines and dark edges on the clothes, especially the jacket.
The hair looks overshaded to me. This is the only part I didn't like. It doesn't match up with the rest of the drawing and also doesn't really seem to add anything to the picture. I'd consider just making it a solid color with a bit of shading, like the rest, and maybe also darken it slightly, but that's just my preference.
Obviously the face isn't supposed to be photo-realistic, but instead stylized, and as such it looks really good.
The birthday card-themed background is relevant and looks great.
I think if he saw this on Twitter he'd really like it.
amg amg amg that's so cute I wanna hug him and touch his hair and his glasses and his everything this didn't sound wrong no I love the pose and his adorkable grin <3 and as always your epic winningatlife drawing style Stay awesome bubbu <3