It's a fine book and a brisk read, but largely obsolescent because everything you could need here is available freely online.
These days TWGBB is more a story of a time gone by, with references to casinos long since demolished, playing conditions that haven't existed for decades, and advice for scenarios that are now exceedingly rare or nonexistent (like decent-stakes home games or charity nights). It's still an enjoyable read in that regard.
One thing I did find very amusing was a brief interview with a Vegas veteran near the end of the book who noted, "...Las Vegas is going downhill... Food is expensive, shows are outrageous... now they're losing the little old lady who faithfully drops $200 a trip several times a year." This was written in 1980 and I'm pretty sure you could've heard some version of that same tale every year in the 45 years since. But the bettors keep coming.