The edit button is only available for a certain amount of time after you make a post.
Anyway, as for the art samples you posted...
The bookshelf sprite is actually constructed very well. It's small, concise, and looks like what it's supposed to be. I would try a more muted palette on it though, the bright colors kind of look a little odd. Also, sprite art is as much about frugality as it is about pixels. Reduce the number of colors down a bit and play with fewer colors. Your sprites will look more cohesive. And you should never ever use jpg compression for small sprites though, it destroys them.
As for the box sprite... well, it really isn't a sprite so much as it's a large drawing of a box.
The other two, the drawn scans, they're not bad if it's a rough style you're going for. It's harder to judge them out of context though. It might be interesting to see an entire game made out of that style of art, but depending on how you go about it could mean the difference between genius and failure. There are plenty of good games out there with rough or crude art, but if it's done right it can add a certain charm to the game. Mainly when making game art, the trick to having it look good is to be rigorously consistent with the look of all your art assets, even if they're crummy.