a) Magoosh has a very well defined structure for Verbal lessons and typically covers everything from basic that a non- native speaker should know to become more sound in solving complex Sentence correction and Critical reasoning questions. Also video explanations after each question are self explanatory and one doesn't need to look for any personal instructor to help with doubts. If in case, there is any doubt, instructors are very polite and clears the doubt with a very holistic approach over email.
b) Quant lessons contain every topic that are covered in GMAT syllabus and questions generally provide exam-like feel.
c) One area of improvement is that user interface can be made little smoother to switch between different sections, but that in no way hinders the study experience in long run.