One thing I learned quickly in client presentations is that design is subjective. Let me repeat that: design. is. subjective. My personal style is not necessarily the same as someone else’s, everyone has their own opinions of what makes a “pretty” site. I also learned quickly to stop thinking of design simply as making things pretty- for the same reason (although I do believe beauty aids usability, but we’ll save that for a different post). Rather, the role of design is to communicate information. I think that’s how you determine if it’s effective, whether or not the information is being communicated effectively.
Look at your ROI. Are your customers using your site? Are they making a full purchase or browsing without buying? Those are the things to look at. That will determine if your web design is working or not.