I play mainly no-limit hold-em. Is TOP mainly limit hold-em book? Or can some of the concepts be applied to no-limit also? Thanks in advance.

TOP isn't a book for any one game. It is a book about the theory of ooker, obviously. It is a typical Sklansky read, though, so if you don't want to study, don't read it. It's lessons ain't coming easily. TOP is good for any form of poker, because it discusses concepts rather than specific plays.

you have to be ready to read this book. if you find it hard to understand or boring then you are not ready for it.

i read as much as possible and when i first started playing i didnt like it. but after time when i got better and finally started to become a winning player and started playing other forms of poker as well as texas hold em i read it and it can be argued that its the single most important book you will ever read.

if you just play poker for fun then its probably not for you. but if you are trying to become the best player you can be or want to go pro one day its a must read.