They aren't that bad, overall, but not great either.
Translation speed varies, but is usually 4 months per volume (note that the time between licensing and the first release can be well over a year though). That's not horribly slow, but when the fan translation is already a lot faster than that, the delay can be pretty painful. There's also the problem when a novel already has something like 20 volumes, and it's not even over yet. In some cases, you're looking at 6+ years just to catch up to the existing translation, and that's assuming Yen Press is around that long and doesn't drop the novel. That's actually one of the biggest concerns, that the official translation might not finish, and by then the interest will have died down to the point that nobody is interested in picking it back up, so it's stalled forever. That hasn't happened much with novels yet (I can't think of an example at least), but it's happened countless times with manga.
In the past, I would have said that the translation quality is a little below fan translations and the writing quality is a little above fan translations (though there are outliers, like NGNL), but in the last couple years it seems that there's been a massive surge of horrible fan translations (and not just machine translations) that are barely readable at best, so YP is looking a lot better in comparison now. Granted, the novels they pick up often have above average fan translations (Skythewood is usually far better than Yen Press, for example, in both speed and quality).