disclaimer: I'm not an expert
Hangul does seem to meet the Wikipedia definition of Syllabary:
a syllabary is a set of written symbols that represent the syllables or (more frequently) moras which make up words.
So now let's see how we can tell syllabaries and abugidas apart.
From the "Differences from Abugidas" section:
In [abugidas], unlike in pure syllabaries, syllables starting with
the same consonant are generally expressed with graphemes based in a
regular way on a common graphical elements...
In a true syllabary there may be graphic similarity between characters
that share a common consonant or vowel sound, but it is not systematic
or at all regular.
In Hangul, characters that share a common consonant or vowel sound have graphic similarity (the consonant part is identical). So far, Hangul is looking like an abugida.
But it's missing a subtle part of what is required by Wikipedia's definition of Abugida
a segmental writing system in which consonant–vowel sequences are
written as a unit; each unit is based on a consonant letter, and vowel notation is secondary. (emphasis mine)
The issue is that vowels are not secondary to consonants in Hangul.
In a true abugida, a single grapheme represents consonant+vowel, and graphemes representing the same consonant are similar, but vowels are not explicitly represented. However, in Hangul vowels are explicitly represented.
To take an example closer to home, we can try to pretend that the English alphabet is an abugida with some harmless gerrymandering. We can slice up "cat" into "ca" (consonant+vowel) and "t" (consonant). And we can also slice up "cut" into "cu" (consonant+vowel) and "t" (consonant). So far, this looks like an abugida, not a syllabary, because the "c" is repeated in "ca" and "cu".
But the illusion is over when we see that we slice "mat" into "ma" (consonant+vowel) and "t" (consonant) because the "a" part is common to both "ma" and "ca", showing that both vowels and consonants are represented, and we're working with an alphabet.
So I think Hangul could fairly be considered:
- a syllabary, since the characters represent syllables
- a featural writing system, since the shapes aren't arbitrary
- almost an alphabet, since it represents consonants and vowels (almost, because the placement of the consonant and vowel parts within a character matter)