i completed the andrew ng course recently, and felt that the difficulty dropped a lot in the second half of the course (for example, he stops giving homeworks). im hoping for more in his new DL courses
I've taken the CNN and RNN (parts 4 and 5) classes of his new DL specialization, and they both area about as rigorous as you wanted. I do have to give a warning though that the last class starts so see some confusing mistakes in the HW. For example, the expected output given is from an outdated HW version.
