At my Taekwondo school, we practice the traditional hyungs as created by General Choi. After reviewing several materials for WTF practitioners and reading books on the history of Taekwondo, I'm left wondering what are the primary differences between the ITF-style hyungs and the WTF poomsae are. Specifically, is one more kick intensive? Stance intensive? What are the key characteristics that differentiate the two styles of pattern (if any!)?
Basically: The Hyungs are chaotic, the Poomsae are well-organized and (mostly) symmetric. Whether this point is in favor of Hyung or Poomsae depends on personal taste, I guess.
The Poomsae have a much smaller technical repertoire, especially, but not only, when it comes to kicks. (Palgwe: Front, Side and Crescent Kick; Taegeuk: Front, Side, Crescent, Roundhouse and Jumping Front Kick; Black Belt Forms: Front, Side, Crescent, Jump-Spinning-Crescent, Jumping Side Kick. This is ridiculously little for an art that claims to be the kicking art)
Personally, I have always wondered how a fascinating art like Taekwondo could come up with a forms system as boring as Poomsae (I hold a 5th Dan WTF, so I know what I am talking about).
At least the newer Poomsae school, Taegeuk, which replaced the older Palgwe school, was also designed to look less like Karate. Large parts of both Hyungs and Palgwe were copied from Shotokan Karate Kata, and that was an aspect the officials liked to hide (after all, TKD was "officially" 2000 years old and had nothing to do with Karate).