Well, if you have much time, and you will definitely to learn Gaelic, the SOL is what you are searching for.
Everything, you are told, can be used on itself ( books, casettes, videotapes); don't trust it and use all together.
It's exellent to provide you with a passive knowledge of Gaelic; in order to build up a working knowledge, to become a fluent speaker, fancy to attend a course at Sabhal Mor Ostaig, or something of the kind.
The book is full of humour, and that is an advantage, if you are trying to learn something.
Warning: the whole serie costs 250 pounds, more or less.