hello: bad, a dictionary word.
h3ll4: bad, because the vowels of the dictionary word "hello" have been REPLACED by the digits 3 and 4.
he22o: bad, because two characters in the dictionary word "hello" have been REPLACED by the digit 2.
he3ll9o or he_ll/o: good, because digits/special characters have been EMBEDDED between the characters of a dictionary word, but have not replaced them.
7he3ll9o or 7he_ll/o: better, because a leading digit has been added to a good password.