It was nice for a while because of all the concrete examples, but why doesn't the book prove anything? Even the proofs that are there are often kind of sloppy and miss important details. It's good for getting the general feel for the representation theory of semisimple Lie algebras (the sl3 example is really nice and you really get a great overall picture from studying it) but not good as a standalone textbook, you'll need another book to give you understandable proofs.