Quality website content, aka web copy or copywriting can be many things to many people. What you might consider to be quality website content depends upon your perspective, what you are looking for in the website, and a number of other things.
There are some general themes that most may be able to agree on like consistency of the message and coherence, technical qualities such as proper grammar and accuracy in description, and a neat format when the website content is displayed.
For example, take a look at this Food Truck website, the content is displayed evenly and coherently.
The website content should convey its purpose well, and work properly.
There are also some negative aspects. For example, a website should not be tacky or have low quality feel to it.
However, the quality of the content is largely subjective and based upon the interpretation of those viewing the website.
What is a quality website? It first must be coherent. This means that the content and the themes of the website have a meaning that is represented throughout the website.
The home page should have information related to the subject of the website, and each subsequently available page should have similar subject matter.
If the subject matter is different, tha is ok, as long as it is explained or has a purpose. If a website is for the purpose of having information on multiple subjects, that’s fine.
Coherency, in the case of a multi-subject website, would mean that all the subjects desired are present; the website doesn’t only have one subject while saying that it has many.
If the page is about a certain type of product, then having a random page about a totally unrelated subject that never explains its presents or relates to the theme of the website might degrade the quality of the website, and potentially reduce the quality of the users experience.
For example, this law firm web design is coherent, it is very clear that it is a law firm offering a variety of legal services.
The grammar used in any text that may appear on the website should be correct. The text must also have proper punctuation and spelling.
Good syntax doesn’t hurt either. The message conveyed should be clear and well worded.
When something is described or explained on the website, the description or explanation should be accurate with regard to the subject matter the author sought to convey.
Consistency is another important consideration. The website must be consistent throughout in its presentation. The font should be the same, for each part of the page on each different page.
For example if each page has a side bar with the same words and links in it, then the side bar should have the same format on each page in which it appears.
The same goes for paragraph headings and text, unless the designer or owner has made a conscientious choice to deviate from this.
Again, many aspects of a website can be of a high quality while deviating from any number of rules about what makes a good website, because the quality of a website is subjective from the point of view of both the owner and the user.