Technical, Understandable, Well Written
The thing about the Mastering series (not to mention Sybex published books) is their artists have allot of technical information to give you BUT they put it out in terms that is understandable to the common non-technical person who's still learning the trade of "Computer Programmer" or "Software Developer". I've been in the field using ColdFusion now for about 6 years and I STILL HAVE trouble understanding everything ColdFusion has to offer. This book tells me everything about what I need to do. The only thing about it I dislike is the fact I need to get yet another one with MX 2004 now hahaha! This was my second book (I have ColdFusion 5 as well)
One last thing and one of the reasons why I go towards the Mastering/Sybex series. The back of the book has a tag reference with all the attributes and their definitions as WELL AS examples in just about every tag reference. THAT my friend is GOLD. If it doesn't give you everything you need to know it at least sets you in the write direction to Google the rest haha.