Well, first, don't use the grass brush unless you are painting grass or some such (even then you really shouldn't use it). Second, don't fall back on filters or effects to create color depth. Use color to do that, color and the paintbrush tool. You seem to be using pen tool alot to define shapes. That's fine if you're doing primarilty vector art, but as a middle ground it doesn't really work well. Maybe if you just refine the look more it may jive better. Take a look at eye anatomy as well, normally the lids cover the irises so as not to create the sensation of staring.
I think right now you're a little too structured. Loosen up a bit. Try the painting tools to define shapes rather than those other, more rigid implements. It is a little difficult at first, but with some effort you can do it.