Kirillov’s [*Elements of the theory of representations*](//ams.org/mathscinet-getitem?mr=412321) is written in quite this spirit. From the original [MR](//ams.org/mathscinet-getitem?mr=407202): 

>The book includes a large number of “exercises” (with hints for proving them), most of them being in fact very nontrivial sketches of results in and out of the literature, or playing an essential role in the proofs of the theorems.