Full disclosure, I knew the creator of the site (though sadly moved away from the 3k era) from days on an old form called Scholars of Shen Zhou. Pinging u/10thousand_stars as their thoughts may also be rather useful for this

Good for the first part of the question in terms of accuracy, I would suggest though more as a useful and free supplementary resource for learning about the era rather then just by itself. I have certainly used it down the years and it is a credit to its creator.

It has free translations of biographies of certain Han figures from Fan Ye's History of the Later Han, a few early civil war figures from the records of the three kingdoms and one or two from the Sima regime from the Tang era Book of Jin. They don't make serious errors with the translations as far as I'm aware and it lines up with other resources I use. You can also get more translations, different translator but more of them as part of an effort to provide a translation of the entire thing, of the records of the three kingdoms elsewhere

It also has a copy of the story of Guan Suo, a fictional work about a fictional son of Guan Yu on it so you will also get a chance to see legends developing. A copy of the novel if you have never read it and a useful list of the sources used in Pei Songzhi's annotations. So a lot of useful resources for people to quickly pick up about history and fiction.

On the wiki part, by being focused on one subject it has managed to keep the public editing problems under control. The issue is not about accuracy but that it depends on what the writers chose to focus on and create and what they haven't had time to do down the years. It does cover aspects not often focused on like earlier fictional works (rather then just not novel) but there are plenty of battles not covered and, for example, figures like Pang Tong are stubs. That isn't a complaint and it is willing to cover less common aspects but if using it for learning about the era, it is something to be aware of.

When Gongjin Campaign Memorial does cover a subject, they do use primary and secondary sources with appropriate citations. Ones with multiple citations can go into a good amount of depth as an overview and with the citations, gives you an idea of where else to explore for a deeper view of the subject.

They try to note some of the fiction of the novel that covers a character, those have been accurate but are little facts rather than providing an overall sense of the fundamental changes. I would go for more neutral tones than they sometimes do in the intro to people but the main thrust of the properly done articles does hold up well.

I have recently suggested a list of other free sources that might help you get started in learning about the era.

I hope that helped and have a good weekend