I've been having tremendous fun writing tutorials about each of the Drupal 8 APIs in turn, and I hope people have been finding them useful. They've certainly been eye-openers for me, as I've always focussed on achieving a clear worked example, and doing that alone unearths all sorts of questions (and usually—but not always—answers) about how Drupal 8's core itself works.
However, as I'm about to start a big project, I'm going to take a break from writing tutorials. They're fun, like I say, but unfortunately they don't pay the bills; they certainly don't keep the cat in the fishy biscuits to which she's accustomed. So the recent post on the database abstraction layer is the last, for at least the foreseeable future. But that means I've covered eighteen of the thirty-six or so featured topics on api.d.o: half-way seems a good point to pause and take stock, regardless!
If you're at all interested in learning Drupal 8's APIs, then do feel free to have a read of some of the posts, as they're not going anywhere, and neither am I, really. Try out some of the worked examples; and like the very kind commenters before you, remember to leave a note about where I might have gone wrong. That way I can fix it for the next reader.
Before I next write a tutorial, then, I might see you at Drupalcamp London instead; just... don't ask me anything too complicated about the APIs!