My biggest suggestion is to make the mouth area smaller. You have everything too enlarged so that's throwing off the right of the proportions out of wack.
A chimera's face isn't THAT too far off from a human. Remember, a vasts majority of chimeras were once human, captured, then turned into chimeras. So if you were to take a basic human skull/face; tack on a set of eyes where the temples would be, and another set just a few inches towards the back and about once inch up from that last set of eyes, that's where the eye placements should be. The eye size itself isn't that much bigger than a human's either, they just have four MORE than a human.
And as far as the jaw line goes, still the same as a human, just no skin from where the side of the lips are to around the back of the jaw. Same idea as the Joker, how he cut his lips, but a bit further, and just imagine if the cuts didn't scar up. That kind of idea.
(The jaw line in the drawing is a bit exaggerated though, to really get that ROOOAARR look)
Then the back of the head is a bit outwards, but not as much as you'd think. It's just moved back enough to be in proportion to if the middle set of eyes were the 'norm' for where the placement of eyes are.
Then the skin that covers the nose area, isn't crazy complicated either. Just thing like Lord Voldemort from Harry Potter, how it's all squished down like that, but with more wrinkly horizontal skin on there instead.
They also have like mini cheek bones under each eye, with the middle cheek bone probably being he biggest because of it's placement.
Then to add teeth to your liking. If you were to cut the face in half, and look at just the right side of the top teeth, the size order starting from the middle of the face outwards would go: medium small, small, HUGE, medium. Then any extras if you'd like. For the bottom half would be pretty much be the same order and size as well.
Here's a doodle I did a few years back then quickly coloured it for the shiggles.
Hopefully it'll give you a better understand of the proportions I'm talking about.
(uncoloured version:
http://fc04.deviantart.net/fs50/i/2009/262/8/3/The_Chimera_by_Hyokenseisou.jpg)
And just fyi, I know just about as much as the chimera as they guys that work at Insomniac, so I know a lot about them. And even if I DON'T know, I can easily ask them as I'm pretty tight with a lot of the guys at Insom, so there's pretty much no info I can't get from them (with the obvious exception of NDA stuff, ie new games coming out.) Proof that I'm tight with Insom? Their new game coming out, Overstrike 9? The red hair character, guess who her first name was named after...
So yeah, don't hesitate to ask.