Undertale Sans sheet!

[DatOneRiley]

What do you think?

[AkumaTh]

Something about these sprites seem off to me but I can't put my finger on it. Two things I can comment on is the following...

The red on the hit seems more like a rope than a wound. It makes it seem less like he's hit and more like he's tied up. And don't have empty space.

[Ton]

It's very pillow shaded with no outlines in some areas, and has solid black lines in others. Maybe that's why it looks weird?

[Garamonde]

http://www.vg-resource.com/thread-25474.html

I'd suggest giving this a read. It won't improve one's spriting skills automatically, but it will educate you on some mistakes spriters often use, so you can improve your sprites.

[Koala]

I'd agree with what the other posters have said so far about it being pillowshaded. I'd also say that the slippers are a bit neon, perhaps tone down the saturation a bit? There are also quite a few jagged lines that could be smoothed out, especially on his pants and jacket. Good start, though!