Ok, I might actually be helpful and tell you how it could be better instead of pointing fingers and laughing like most people do.
The monkey's decent, at least the linework is, but as the others said, you need some shading. Pick a tone of the same brown you've used that's a bit lighter, and another that's a bit darker. Make sure they have enough contrast so that you can actually distinguish them from each other, but not too much contrast or you'll put focus on the wrong spots.
You've done some minor shading, but to shade properly you need to pick a lightsource (ie. a point from where light is coming from). Say you've picked the top left (or 'north-west'). All 'north-west' bits of the monkey that would be exposed to the light (not 'indented' bits, such as armpits) should be shaded the ligher tone, whilst bits that would be hidden from the light due to the monkey's psuedo-3D properties should be shaded the darker colour. It sounds like a pain in the arse but the end result is well worth it. I might whip something up using your lineart later, if you don't mind, just to show you an example.
Another thing to consider is using dark hues of colours for the 'outlines' rather than black. Black's good for the initial lineart, but for a finished product it can make it look like your work is divided into 'sections', which can reduce the overall quality of your work. Black outlines are good for cartoon-ish pieces though, depending how colourful your work is.
If you're looking to increase your skills, visit www.pixelation.cjb.net for a little while and submit some of your work there. People there actually comment with constructive stuff instead of just saying "you need more practice" and they will teach you step by step how to pixel like a pro, or at least make it look like you do.