I'm interested to hear whether Encarta did have articles on anal sex and principal component analysis; the slice of Wikipedia I have here is only 45,000 articles, and Encarta was 32,000, so it's surely possible. I doubt that it does, though.

Encyclopedias in general are not primary sources; they're secondary and tertiary sources. Generally speaking, it's not a good idea to try to evaluate the primary sources in a field unless you already understand the field reasonably well, because primary sources are mostly wrong or misleading in ways that can be hard to detect, and this is why we prefer secondary sources for Wikipedia sources most of the time. (Perhaps you don't know what a primary source is; see https://en.wikipedia.org/wiki/Primary_source.) None of this is a significant difference between Wikipedia and Encarta or Britannica, except that Wikipedia cites many, many more sources.

In empirical studies, Wikipedia was found to contain about the same level of errors as Britannica in areas that both encyclopedias covered, but that was many years ago; Wikipedia has improved substantially since then. At this point most of the accusations of major errors in Wikipedia come from Holocaust denialists, anti-vaxxers, and the like.

It's true that every Wikipedia editor has biases, but for their edits to survive, the edits need to be acceptable to editors with very different biases, or be in a place that nobody ever looks (as with the Seigenthaler affair). That's what accounts for the sometimes annoying Wikipedia style where every strong assertion is followed by a plethora of qualifications and exceptions. Encarta and Britannica never had this advantage, so errors and egregious biases sometimes persisted during many years.

So it's not true that Wikipedia is less trustworthy than Encarta and Britannica — rather the contrary, except in the short interval before vandalism gets reverted — and it's not true that you should trust your interpretation of primary sources on health matters or business matters over Wikipedia's interpretation, unless you know a lot about medicine or business. Following links from Wikipedia to secondary sources like Cochrane Collaboration reports or Bloomberg articles is a much better idea.

It's also not true that Wikipedia doesn't have multimedia, or only recently acquired multimedia. The PCA article I used as an example above has six illustrations, and the SVD article it links to has a very helpful animation at the top of the article, an animation which dates from 2010, as well as a couple of other visualizations, and a whole lot of equations. (You could maybe argue that six illustrations isn't very many for 30 pages of text full of equations, but illustrating high-dimensional linear algebra is kind of difficult.) What it doesn't have is interactivity: there's no way to modify a data set and see how that changes its PCA, or even just to explore the PCA of an existing immutable dataset.

The anal sex article, in addition to 14000 words and 139 references, contains a fairly graphic level of multimedia content — 13 detailed illustrations, including photographs of artifacts from many historical cultures — but no animations and fortunately no interactivity either. It's a Level 4 Vital Article, meaning that it's among the ten thousand or so most important articles in the whole encyclopedia. (PCA is not.)

I suspect that what's going on here is that, even though Wikipedia has more multimedia than CD-ROM Encarta (by two or three orders of magnitude), it exceeds Encarta's textual contents by an even larger factor, so it appears to be light on multimedia, just by contrast. But I never used Encarta, so I could be wrong about that? (I went straight from MS-DOS on a 286 to the internet.)

I definitely agree that Wikipedia is not a substitute for having the rest of the web at your fingertips.