yes- i'm a TEXTBOOK Aquarius lol- cusp born with Capricorn, first decant. Moon in Scorpio, Cancer rising.
many people don't understand WHY it works, though i do and it takes volumes of writing to explain so i won't here- but suffice to say, its abstract and has to do with metaphysics concerning the interconnectedness of everything, and at its simplest, the ancient adage of 'as above, so below; as below, so above; in the unity of the One Thing.' meaning, macro and microcosms are intimately entwined and reflect each other. the universe is a living body, as we are miniature universes, and they mirror each other.
the main criticism of the system is from people who don't entirely see themselves in their own sun sign's description. what we have to remember though, is that the sun sign doesn't determine everything about you (or there'd only be 12 types of people in the world)... rather, its a skeletal framework upon which everything else is built, heavily influenced and modified by sex, cusps and decants, moon sign, ascendent sign, the positions of the planets at the moment of birth, what houses they fall into in the sky's divisions, what signs they fall under in a natal chart, how they interrelate to each other, etc... it gets complex. so complicated, in fact, and specific, that even twins born moments apart would have slightly different natal charts, resulting in different personalities and destinies. the likelihood of two charts being identical is something ridiculous like one in several hundred billion. even people born on the same date at the same time would have completely different charts if they're at different LOCATIONS because, obviously, the heavens look different depending on where one stands.
as to the issue some bring up of 'vagueness' making each sign applicable to anyone who WANTS to see themselves in it.... any astrological work of value will not be so vague, and furthermore, that issue is addressed above- the vagueness is entirely weeded out as more layers of depth and influence are factored in. i've not yet met a person who didn't think my natal chart for them wasn't freakishly 90-some percent accurate, down to tiny details and unique personality quarks. and i'm not even very good at it.
in any case, i think many people knock it cause they don't understand it, or haven't come across any astrological work of quality.... much like homophobes' and their incomplete opinions of gay men.