This is one of those books that I keep coming back too. Not because it is easy and fun, but because it is hard. When you look through it, well it always seems easy. However trying it out is another story.
The book is really for those seriously into Botanical Illustration, if your idea is just painting blue flowers, then it is probably the wrong thing. If your wanting to get into scientific illustration, then it is probably one of the best places to start. If only to see the standards required.
The emphasis is on watercolour, but really anyone who is patient and works through it will benefit.
Definitely worth getting.