Very enjoyable. He wisely eschews the writing of a properly-so-called biography, done to death of course (see the excellent, much later one by Hibbert, or of course Boswell's own!), and focuses on other aspects while still bringing Johnson's life to...life.
I picked it up because it's by Leslie Stephen, and I was curious to see how he wrote: very well, as it turns out, in that late, late 19th-century English style, inimitable really.
And it's worth the price of admission for lines like these alone:
'[Johnson’s] most ambitious work, Irene, can be read by men in whom a sense of duty has been abnormally developed'.
one almost wishes his daughter had been so funny :)