Lets see if i can be of some help, I've done a few skulls with rather good results.
First of, the nose and eye sockets should not be back grounded, it's actually bones in the background too in various pieces or/and shapes,l i think that's one of the reasons it looks a wee bit off.
Like Kevin says, the modeling tools, make sure to use them often:-) These are some of the most important tools at all when doing figure carving/tooling. Except for the bevellers this is the tool I use the most. Then
The sides of the nose...Think in 3D, the nose needs to "poke out" so some pear shading around the edges will work...I'll paste in some photos that I hope will explain better than I can