First of all, I like it. I like the whitespace, the heading font—it gives kind of an old-school feeling with a modern touch.
The paragraph text under "Client reviews" and "News & events" is tiny though. I like it in the footer, just feels a bit too small in the paragraphs. And I'd like to see some more balance in the line-height (leading). Line-height under "Latest work" is a bit tight, same in the slides, but under "News & events" it's pretty loose instead. I'd like to see something in-between—more balance and consistency.
But again, I like it. The color palette is nice in my opinion, feels nice and smooth to read. The font-size again is a little small though. Check out Huge Inc. for example, they've got a small font-size in the footer and other areas but the important content is slightly larger, which makes it easy to read.
Firstly it took a while to load for me so that is something you should look into. Is it an issue with the server or the design? Cut back the load time (or then again it could be my internet speed.) I think you need a better logo far too basic, advertising agencies usually have really flashy, well designed logos and yours is just basic text. The lined border looks awful in my opinion get rid of it! Negatives aside the website is well layed out, easy to navigate, doesn't strain the eyes, nice use of clipart and photography to send out a message.
At the moment I would give the website 5/10. It is a decent solid website but the advertising world is highly competitive you need a design that is high impact, captures attention and displays a powerful message. I dont want to be harsh, just trying to help you improve the website.