Below I am specifying all factors which can make any website called good one with point of its design and development.

Web design which gives same performance in all browser (Firefix,IE, safari) and device( laptop, desktop, Ipad).
Website which load quickly and which performs all the operation quickly on user action or any event
Web design with use of latest technology like HTML5 and CSS3.
Error free Web coding of HTML and CSS and which also get validated through W3c standards.
Good interface which make complex functionality of the website simple when it comes to user experience.
Website built with Easy to use CMS for good admin interface and to manage database task efficiently.
Strong URL and site architecture to compete with other websites
Websites with low bounce rate