I'm reading it. I love it. I think the movies did a really good job with their adaptation. The best lines - like Captain Keene's epic Shaming of Simpson - are lifted straight from the book. (Except for Archie's lines, of course, which are much better than their non-Archie book versions.) Horatio is as geeky, gangly, and over-dramatic as the boy we all love from fan fiction.
The funny thing is that, by this point, I've read so much Hornblower fan fiction that reading the original feels like reading another fanfic. "Ooh, more Justinian fic! I love it!" It gives those extra fanfic-y details, like the fact that Horatio (and Archie of course, since they're only six months apart as we all know) really were the youngest midshipmen in the berth - Hether and Cleveland were much older. It's just that the author inexplicably got some of the names wrong, and forgot to mention Archie. I'm sure he was really there.
I do have to admit, though, that I don't think teenage Horatio would have been quite so wrapped in dramatic adolescent suicidal gloom if he'd had a certain smiling ball of sunshine by his side. If Archie were there, that kill-or-be-killed instinct would be better explained by the desire to protect Archie as well as himself.
lemurling explored this really well.
Anyway, I haven't read the series in at least two decades, so it's nice to go back to it!