It looks very nice! I quite like the ghostly blue-white you're using (and that 3D object is sweet as well).

I do understand the comments that say it looks like OS9, though - the reason is very simple...

Rather than take advantage of Aqua's built-in window stroke and drop-shadow to define your window edges, you're defining your edges with black lines, which was pretty much the norm with OS9 (seeing as it had no built-in strokes or dropshadows to take advantage of). Unfortunately this will always look a bit wonky to many people's eyes as many of Aqua's main interface elements (dropdown toolbars, menus, dialog backgrounds) won't feature the stroke. Aqua was built to be photorealistic more than illustrative, so it will always look more pleasing to most people's eyes when a theme is built with that in mind.

You could even go photoreal with the materials you're using... your overall design itself - in terms of line and proportion and colour choice - is actually flawless. It just looks illustrated rather than rendered (nothing wrong with that, but it can look a bit wierd with Aqua). You could always push those pixels out to the window edges and limiting your strokes to interior regions of the window. You could try resampling up 200% and then back down 50% to soften the details a wee bit. With the nice hazy plastics you're using (using the 3D object for reference), you wouldn't really even see any true black in the shadow details... Look to real world materials or 3D rendered lighting/surfacing tests for ispiration and have fun trying to recreate them.

I also find it's helpful to create a compound layer effect with a slight semi-transparent stroke, slight outer glow set in transparent black to multiply, and a drop-shadow (look to aqua and try your best to match it) and design with it turned on to get a feel for how the final window headers, etc. will render in-system... I'll just turn these off before building the actual resources... you can do the same for buttons as well (but leave these turned on and merge them with the actual pixels before buidling into the resouces - as long as you understand how to derive masks and premultiply from a merged layer, no problemo).

My 2�... again, nice design