The Minna No Nihongo series is not for the casual learner. It requires discipline. It explains grammar in linguistic terms and expects you to memorize patterns through repetition.
If you are looking for organized N3 grammar guides similar to the Minna No Nihongo style, these are the most effective alternatives: Minna No Nihongo Chukyu I & II Minna No Nihongo N3 Grammar Pdf REPACK