Some problems with Flear's book are discussed here.

I didn't like Sadler's books at all. I don't like the format. Too much discussion about obvious things and not enough analysis of the upcoming middlegames. He's also skipping too much on common lines like the Qc2+g4 and Qc2+e4 in the semi slav and the e4 gambit in the slav.

Wells wrote a much better book on the semi slav, but it is a bit old now, and I much preferred Burgess' book on the (regular) slav.

Sadler's semi-slav book is great for what it has, but I just remembered there is one problem: the coverage of 6. Bh4 Anti-Moscow is almost non existent  In current practice, this variation is probably the most important in the whole 5. Bg5 Semi-Slav! Pedersen is indispensable here. there are so few semi-slav books around you might as well get them all.

I have not seen Flear's earlier Slav book as it was published before I even started playing chess!

Sadler's two books Slav and Semi-Slav is still best today for learning the openings.Of course the lines are outdated, but the verbal explanations of ideas are timeless. I have them in their Chess Press editions circa 1997-98(?), and to my knowledge these two have not been updated. While Sadler's Slav book has received good reviews, there is somewhat less talk about his Semi-Slav volume, but I find it even better than his Slav book!   

Just received the book a week ago. This book is decent, but not ground-breaking, and in fact I was slightly disappointed considering Flear's reputation as a slav expert. 

To begin with, the theory is sketchy. I could count at least a dozen lines missing. Okay, maybe this is a starting out book, but still, a mention wouldn't hurt!? 

Exchange Slav: Flear only covers 6... a6 (is this a repertoire book?), but he does not cover the rather critical 3. cd5 cd5 4. Nf3 Nf6 5. Nc3 Nc6 6. Bf4 a6 7. Rc1! as used by Graf. Imho this is a serious omission.

Main Slav: 4... dc4 5. a4 Bf5 6. Nh4: only covers 6... e6 and 6... Bc8. 

6. Ne5: no mention of 7... Nb6. 

Morozevich's 11... g5: no mention of Jobava's strong 12. Bxe5!?

Early e3: no mention of 3. Nc3 Nf6 4. e3 Bg4!? recommended by Burgess, and the subject of a TWIC Theory article by Prie. 

...a6 slav: only 5. c5, 5. e3, 5. a4 covered.

Botvinnik/Moscow: As typical in the rest of the book, Flear only covers the main lines, with little to no coverage on minor lines.  Flear recommends 12... Qc7 Botvinnik, but he only shows the pioneer game V. Mikhalevski-Shabalov 2003, where White was clearly surprised and played badly.

Shabalov's 7. g4: only 7... Bb4 covered, and brief mention of consequences of 7... Nxg4.

I could go on and on. The root of the problem is that the subject matter is too wide. It would have been better for the Slav to be in one volume, and the Semi-Slav in a separate volume. 

On the plus side, Flear covers the hybrid e6/a6 meran (the first time it has received coverage in any book?), and the Schlecter Slav receives an impressive treatment, as good as I've seen anywhere. 

There is also some coverage of the Marshall and Noteboom, though far from exhaustive. It is also interesting to read bits and pieces of Flear's opinions here and there. e.g. he thinks 11...Qa5 Botvinnik is a good try for Black.
 
Overall I can't really say this book is a must-buy. It's missing Sadler's detailed verbal explanations, and Burgess/Pedersen's theory, and to me it ended up slightly the worst of both worlds. It is saved by good coverage on certain lines, and of course a reknowned expert's general opinion on which lines are good/bad is always interesting. In these respects, Flear's book reminds me of Kasparov's QGD DVD. 

Overall I would give this book a rating of 3/5. If you are starting out in the slav/semi-slav, Sadler's two books are still best.

Anybody else seen this book?