Joe Gallagher writes a nice chess book; check out Winning with the King's Gambit if you are into that sort of double edge opening. I can see that soon this will get over my head. I am on Section 1 which is the easiest and they appear to be about equal to the level 20 of CT-Art. Toward the end, I am sure they have the difficulty of the New York Times Sunday Crossword. I will be scanning the puzzle and going to the answer soon after.....
Don't bother with this one unless you're a strong tournament player already. Many of the puzzles in the last part of the book are just ridiculously difficult (10-11 move long lines - 20+ ply - are not uncommon), and more than a few of them are from games where strong grandmaster's overlooked the winning continuation.
I did have a look at all the problems in the book, but I didn't work as hard on all of them as the author probably had intended me to do; I think it's more or less worthless to spend a lot of time on complicated positions involving hidden tactical resources that a strong GM like e.g. Loek Van Wely overlooked during the game - if he overlooked it, so will I, and reading a book like this one won't matter one bit. In most real games you don't have time to calculate such lines out anyway, and so you're often better off employing a more pragmatic approach and avoiding the critical line which can easily backfire.
I think training tactics using books like this one is in general inferior to using online tactics trainer resources such as chesstempo or the tactics trainer implemented on playchess, which is part of why it took me so long to finish the book. Most online resources make use of time constraints, and this is crucial because figuring out when to stop calculating is really important. Spending too much time on a position is a real risk which can easily lead a player to losing a game, and reading books like this one may easily cause players to adopt/establish bad calculation habits and decision-heuristics which increase the probability of such an outcome. The author does try to implicitly address the problem of time constraints in the very last part of the book, but it's in my opinion too little, too late.