The interesting part about Hangeul isn't so much so that it's phonetic - that property is not that uncommon; e.g. modern Serbo-Croatian and Macedonian orthographies are about 99% phonetic. It's that it's featural, meaning that the shapes of the letters are mnemonic and represent their sound values and/or relations between them (e.g. vowel harmony).

Featural scripts are pretty rare - it seems that they never evolve naturally, so it's something that has to be constructed, and then also to become popular for long enough to stick around. The only example I know of other than Hangeul is https://en.wikipedia.org/wiki/Canadian_Aboriginal_syllabics, and they are noticeably less featural.

(Featural scripts for conlangs are more common - e.g. for Lojban, there's Zbalermorna: https://jackhumbert.github.io/zbalermorna/write-up/)

One thing to keep in mind though is that Hangeul was very systematic and consistent back when it was designed. But languages evolve, and they evolve much faster in the absence of widespread literacy and mass media. And Hangeul is almost 600 years old now. So e.g. ㅐ was originally the diphthong "ai", consisting of ㅏ for "a" and ㅣ for "i", but it's now pronounced "e" - not dissimilar to English, actually, but with much more rapid and drastic changes. At this point, it's actually less phonemic than Serbo-Croatian.