It should be clean, well organized, straight to the point and properly coded. Always keep in mind that less is more so as much as possible avoid unnecessary elements that could ruin the sites overall look and functionality, but of course there is always an excemption to the rule as sometimes you need to go all out. Be creative and pay attention to details.
Here's one of my personal site(shameless plug) www.andrewpaglinawan.com can't say its professional enough but im quite happy with the outcome.
ei, just a constructive criticism.. i think gray and pink don't go hand in hand, well, at least in your case. try to polish the images more and avoid overusing gradient. those pink buttons are quite pixelated for me, try fixing it and it would be a nice site.
usually professional ones have good graphics and have up to date trends, such as the very famous one, web 2.0
web 2.0 just consists of very basic looking symbols with light effect and bright colors. usually you can just search on good web 2.0 designs and look up on it from there.
and yes, they are extremely easy to navigate through. (and the colors blend well)